CINXE.COM

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head profile="http://gmpg.org/xfn/1"> <title>Computational Organic Chemistry » 2014 » September</title> <meta name="google-site-verification" content="g1Myv4tUVAmqRbwZeBi7IPuSZpP64RWjVJ6itIoouCo"> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> <style type="text/css" media="screen">@import url( /blog/wp-content/themes/comporg/style.css);</style> <link rel="stylesheet" id="wp-block-library-css" href="/blog/wp-includes/css/dist/block-library/style.min.css?ver=5.6.1" type="text/css" media="all"> <script type="text/javascript">  </script> </head> <body> <div id="header"> <div id="header_img"></div> </div> <div id="link_section"> <div style="float:left"> <a href="/blog/about">About this Blog</a> | <a href="/">Book Homepage</a> | <a href="http://www.wiley.com/WileyCDA/WileyTitle/productCd-0471713422.html">Purchase the Book</a> </div> </div> <div id="after_links"></div> <div id="content"> <div id="main"> <h2 class="post-title">Archive for September, 2014</h2> <div class="box"> <h2><a href="/blog/archives/3226" rel="bookmark" title="Permanent Link: Diels-Alder reactions of Fullerene">Diels-Alder reactions of Fullerene</a></h2> <div class="post-content"> <p>Diels-Alder reaction involving fullerenes have been known for some time. They occur across the [6,6] double bond of C<sub>60</sub>, the one between two fused 6-member rings. Houk and Briseno report on the Diels-Alder reaction of C<sub>60</sub> with pentacene <b>1</b> and bistetracene <b>2</b> and compare their computations with experiments.<a href="#fullereneDA"><sup>1</sup></a></p> <p align="center"><img src="/blog/wp-content/fullereneDA.png"><br>Pentacene and bistetracene ring numbering convention</p> <p>Computations were performed for the reaction of <b>1</b> and <b>2</b> with C<sub>60</sub> at M06-2x/6-31G(d)//M062x-3-21G*. The reaction can occur with the dienophile being either ring 1, 2, or 3 of pentacene and ring 1, 2, 3, or 4 of bistetracene. They located TSs and products for all of these possibilities. Select TSs and products are shown in Figure 1.</p> <p>For the reaction of <b>1a</b>, the lowest energy TS is for the reaction at the central ring (ring 3), and the resulting product is the lowest energy product. The transition state (<b>PT_TS3</b>) is shown in Figure 1. This TS has the least distortion energy of the three possibilities, because reacting at this central ring destroys the least amount of aromaticity of pentacene. For the reaction of <b>1b</b>, the lowest barrier is again for reaction of ring 3 (through <b>TMSPT_TS3</b>). However, the product from the reaction with ring 2 (<b>TMSPT_P2</b>) is lower in free energy than <b>TMSPT_P3</b>, likely caused by steric interactions with the silyl substituents. This actually matches up with experiments which indicate that an analogue of <b>TMSPT_P2</b> is the kinetic product but <b>TMSPT_P3</b> is the thermodynamic product.</p> <table align="center" border="0" cellspacing="0" cellpadding="3"> <tr align="center" valign="bottom"> <td colspan="2"> <p></p> <div class="jmol" id="PT_TS3"> <a onclick="return false"><br> <img src="/blog/wp-content/PT_TS3.jpg" onclick="insertJmol('PT_TS3',300,300,'PT_TS3.xyz')"></a> </div> <p><b>PT_TS3</b></p> </td> </tr> <tr align="center" valign="bottom"> <td colspan="2"> <p></p> <div class="jmol" id="TMSPT_TS3"> <a onclick="return false"><br> <img src="/blog/wp-content/TMSPT_TS3.jpg" onclick="insertJmol('TMSPT_TS3',300,300,'TMSPT_TS3.xyz')"></a> </div> <p><b>TMSPT_TS3</b></p> </td> </tr> <tr align="center" valign="bottom"> <td> <p></p> <div class="jmol" id="TMSPT_P2"> <a onclick="return false"><br> <img src="/blog/wp-content/TMSPT_P2.jpg" onclick="insertJmol('TMSPT_P2',300,300,'TMSPT_P2.xyz')"></a> </div> <p><b>TMSPT_P2</b></p> </td> <td> <p></p> <div class="jmol" id="TMSPT_P3"> <a onclick="return false"><br> <img src="/blog/wp-content/TMSPT_P3.jpg" onclick="insertJmol('TMSPT_P3',300,300,'TMSPT_P3.xyz')"></a> </div> <p><b>TMSPT_P3</b></p> </td> </tr> <tr align="center" valign="bottom"> <td> <p></p> <div class="jmol" id="BT_TS2"> <a onclick="return false"><br> <img src="/blog/wp-content/BT_TS2.jpg" onclick="insertJmol('BT_TS2',300,300,'BT_TS2.xyz')"></a> </div> <p><b>BT_TS2</b></p> </td> <td> <p></p> <div class="jmol" id="BT_P2"> <a onclick="return false"><br> <img src="/blog/wp-content/BT_P2.jpg" onclick="insertJmol('BT_P2',300,300,'BT_P2.xyz')"></a> </div> <p><b>BT_P2</b></p> </td> </tr> </table> <p align="center"><b>Figure 1</b>. M06-2x/3-21G* optimized geometries.<br>(Once again a reminder that clicking on any of these structures will launch JMol and you’ll be able to visualize and manipulate this structure in 3-D.)</p> <p>The computations involving the Diels-Alder reaction of C<sub>60</sub> with either <b>2a</b> or <b>2b</b> come to the same conclusion. In both cases, the lowest barrier is for the reaction at ring 2, and the product of the reaction at this same ring is the only one that is endoergonic. The geometries of <b>BT_TS2</b> and <b>BT_P2 </b>are shown in Figure 1. More importantly, the barrier for the Diels-Alder reaction involving <b>2a</b> and <b>2b</b> are at least 6 kcal mol<sup>-1</sup> higher than the barriers for the reaction of <b>1a</b> and <b>1b</b>, in complete agreement with experiments that show little reaction involving analogues of <b>2b</b> with C<sub>60</sub>, while analogues of <b>1b</b> are reasonably rapid.</p> <h3>References</h3> <p><a name="fullereneDA"></a></p> <p>(1) Cao, Y.; Liang, Y.; Zhang, L.; Osuna, S.; Hoyt, A.-L. M.; Briseno, A. L.; Houk, K. N. "Why Bistetracenes Are Much Less Reactive Than Pentacenes in Diels–Alder Reactions with Fullerenes," <i>J. Am. Chem. Soc.</i> <b>2014</b>, <i>136</i>, 10743-10751, DOI: <a href="http://dx.doi.org/10.1021/ja505240e">10.1021/ja505240e</a>.</p>  </div> <p class="bottom"> <span class="cat"><a href="/blog/archives/category/reactions/diels-alder" rel="category tag">Diels-Alder</a> &<a href="/blog/archives/category/molecules/fullerene" rel="category tag">fullerene</a> &<a href="/blog/archives/category/authors/houk" rel="category tag">Houk</a></span> <span class="user">Steven Bachrach</span> <span class="date">29 Sep 2014</span> <span class="comments"><a href="/blog/archives/3226#respond">No Comments</a></span> </p> </div> <div class="box"> <h2><a href="/blog/archives/3303" rel="bookmark" title="Permanent Link: Becke’s <i>Perspective</i> on DFT">Becke’s <i>Perspective</i> on DFT</a></h2> <div class="post-content"> <p>The <i>Journal of Chemical Physics</i> has produced a Special Topics issue on <i><a href="http://scitation.aip.org/content/aip/journal/jcp/140/18/section?heading=SPECIAL+TOPIC%3a+ADVANCES+IN+DENSITY+FUNCTIONAL+THEORY">Advances in Density Functional Theory</a></i>. I want to call to your attention the Perspective article by Becke titled “Perspective: Fifty years of density-functional theory in chemical physics”.<a href="#BeckeDFT1"><sup>1</sup></a> Becke writes a personal account of the history of DFT and makes a number of interesting points and observations. He rightly notes that DFT is exact and we should more properly refer to our actual implementations as Density Functional Approximations (DFA). He also notes that use of the term <i>ab initio</i> as a synonym for wavefunction theory is inappropriate as DFT is just as <i>ab initio</i> as HF and post-HF theories.</p> <p>A common perception about DFT (well, DFA) is that there is no way to systematically improve functionals. Becke exposes a true underlying logic that <i>has</i> driven much of DFA development.</p> <p>Lastly, Becke is discouraged by the more recent developments that have included virtual orbitals, such as double hybrid methods. His approach is that true DFT is <i>occupied orbitals only</i> (for which he pointedly does not want to adopt the acronym <i>OOO</i>), and that developments that include the virtual orbitals might toll the “death knell” for DFT.</p> <p>For those interested in a pretty accessible account of the history of DFT, Becke’s <i>Perspective</i> is an excellent place to get started.</p> <h3>References</h3> <p><a name="BeckeDFT1"></a></p> <p>(1) Becke, A. D. "Perspective: Fifty years of density-functional theory in chemical physics," <i>J. Chem. Phys.</i> <b>2014</b>, <i>140</i>, 18A301 DOI: <a href="http://dx.doi.org/10.1063/1.4869598">10.1063/1.4869598</a>.</p>  </div> <p class="bottom"> <span class="cat"><a href="/blog/archives/category/qm-method/dft" rel="category tag">DFT</a></span> <span class="user">Steven Bachrach</span> <span class="date">24 Sep 2014</span> <span class="comments"><a href="/blog/archives/3303#respond">No Comments</a></span> </p> </div> <div class="box"> <h2><a href="/blog/archives/3256" rel="bookmark" title="Permanent Link: Looking at “stability” – the role of tunneling">Looking at “stability” – the role of tunneling</a></h2> <div class="post-content"> <p><b>1</b> is notable for its very short central C-C bond, computed at B1B95/6-31G(d) to be only 1.30 Å. Also notable is that <b>1</b> can rearrange to the carbene <b>2</b> with a release of considerable energy (Δ<i>E</i>=-105.4 kcal mol<sup>-1</sup>). Nonetheless, the barrier for this rearrangement is 6.7 kcal mol<sup>-1</sup> suggesting that <b>1</b> might be stable and isolable at low temperatures. (See <a href="/blog/archives/2888">this previous post</a> for more discussion on this rearrangement, including interactive molecules.)</p> <p align="center"><img src="/blog/wp-content/JackInBoxI1.png"></p> <p>Kozuch has now examined this rearrangement in more detail, to see if <b>1</b> is really stable.<a href="#JackInBox1"><sup>1</sup></a> The issue he raises is the role of quantum mechanical tunneling – since the distance that the carbon atoms need to move in reaching the TS is rather small, perhaps heavy atom tunneling might manifest. In the absence of tunneling, conventional variation transition state theory (CVT) predicts that the half-life of <b>1</b> is 170 s at 75 K, and longer still at even lower temperatures. However, the situation is radically different when tunneling is included. Accounting for tunneling using the small curvature tunneling (SCT) approximation predicts a half-life of 1.6 x 10<sup>-3</sup> s at 75 K and only a minimally longer half-life of 4.6 x 10<sup>-3</sup>s at 10 K. Thus, Kozuch concludes that <b>1</b> is not stable at any temperature! One should thus be cautious in applying the term “stable” to a compound that might be quite strained and susceptible to tunneling.</p> <p>(As an aside, Kozuch also notes that <b>2</b> can rearrange into <b>3</b> and this rearrangement also has a very short half-life on the order of milliseconds at cryogenic temperatures. The structure of <b>3</b> is shown in Figure 1.)</p> <p align="center"><img src="/blog/wp-content/JackInBoxI2.png"></p> <table align="center" cellspacing="0" cellpadding="0"> <tr align="center"> <td> <p></p> <div class="jmol" id="JIB3"> <a onclick="return false"><br> <img src="/blog/wp-content/JackInBox3.png" onclick="insertJmol('JIB3',300,300,'JackInBox3.xyz')"></a> </div> </td> </tr> </table> <p align="center"><b>Figure 1</b>. B1B95/6-31G(d) optimized structure of <b>3</b>.</p> <h3>References</h3> <p><a name="JackInBox1"></a></p> <p>1) Kozuch, S. “A Quantum Mechanical “Jack in the Box”: Rapid Rearrangement of a Tetrahedryl-Tetrahedrane via Heavy Atom Tunneling,” <i>Org. Lett.,</i> <b>2014</b>, <i>16</i>, 4102-4105, DOI: <a href="http://dx.doi.org/10.1021/ol5017977">10.1021/ol5017977</a>.</p> <h3>InChIs</h3> <p><b>1</b>: InChI=1S/C14H12/c1-2-8-11-5-3-9-7(1)10(9)4-6-12(8,11)14(8,11)13(7,9)10/h1-6H2<br>InChIKey=LNBZAENQMFDBJW-UHFFFAOYSA-N</p> <p><b>2</b>: InChI=1S/C14H12/c1-3-11-12-4-2-9-7-8(1,9)10(9)5-6-13(11,12)14(10,11)12/h1-6H2<br>InChIKey=UKVODHRLGFPZPT-UHFFFAOYSA-N</p> <p><b>3</b>: InChI=1S/C14H12/c1-2-10-8-12(10)4-3-11-7-9(1,11)13(11)5-6-14(10,12)13/h1-6H2<br>InChIKey=AATRYSJRWFKWAY-UHFFFAOYSA-N</p>  </div> <p class="bottom"> <span class="cat"><a href="/blog/archives/category/tunneling" rel="category tag">Tunneling</a></span> <span class="user">Steven Bachrach</span> <span class="date">22 Sep 2014</span> <span class="comments"><a href="/blog/archives/3256#respond">No Comments</a></span> </p> </div> <div class="box"> <h2><a href="/blog/archives/3306" rel="bookmark" title="Permanent Link: Data emancipation">Data emancipation</a></h2> <div class="post-content"> <p>Readers of my blog know that I am an advocate for <a href="http://en.wikipedia.org/wiki/Open_data">Open Data</a>, whereby scientists permit the widespread distribution of data without restrictions. Data should be available to anyone at any time at no cost without any legal (i.e., copyright or IP) restrictions. This will enhance our abilities to follow up on research and reuse the data in whatever way we wish. In particular, reuse of data should be seamless and lossless.</p> <p>I have noted many times that Supporting Materials in today’s journals is far from ideal. Often authors do not include data at all! Sometimes the data is corrupted, especially if data is being deposited solely through pdf, which involves the loss of almost all semantic information about the data. Unfortunately, very rarely is data deposited in a form that is readily reusable. For example, I make use of 3-D coordinates of molecules for this blog, and these are invariably deposited as simply text within a pdf. I then have to copy-and-paste this data into a new file formatted for use in some molecular viewer of my choice (for me, typically GaussView or Avogadro).</p> <p>The leader in advocating and demonstrating chemical data reuse is Henry Rzepa (see <a href="http://www.ch.ic.ac.uk/rzepa/blog/">his blog</a> for many examples). He and his group have published a paper describing a system for separating data from the paper narrative – a process they call <i>data emancipation</i> – as part of the scientific publication process.<a href="#dataEmanc1"><sup>1</sup></a> I strongly encourage readers of this blog to take a look at this paper for the publication model they propose that places data at the nexus of the scientific process and makes it available for widespread reuse. Take a look at the web enhanced objects, such as <a href="http://pubs.acs.org/doi/media/10.1021/ci500302p/ci500302p_weo_002.htm">this one</a> (you might need a subscription to access this, but <a href="http://doi.org/10.6084/m9.figshare.840483">this link</a> takes you to the Figshare site which is open), to see how data can be deposited for search, retrieval, and direct reuse. This is a model I hope many computational chemists will adopt. We also need to advocate with journal editors and publishers to establish similar procedures for <i>all</i> manuscript submissions.</p> <h3>References</h3> <p><a href="#dataEmanc1"></a></p> <p>(1) Harvey, M. J.; Mason, N. J.; Rzepa, H. S. "Digital Data Repositories in Chemistry and Their Integration with Journals and Electronic Notebooks," <i>J. Chem. Inf. Model.</i> <b>2014</b>, ASAP, DOI: <a href="http://dx.doi.org/10.1021/ci500302p">10.1021/ci500302p</a>.</p>  </div> <p class="bottom"> <span class="cat"><a href="/blog/archives/category/e-publishing" rel="category tag">E-publishing</a></span> <span class="user">Steven Bachrach</span> <span class="date">17 Sep 2014</span> <span class="comments"><a href="/blog/archives/3306#comments">1 Comment</a></span> </p> </div> <div class="box"> <h2><a href="/blog/archives/3243" rel="bookmark" title="Permanent Link: Fullerene oligomers as electron traps">Fullerene oligomers as electron traps</a></h2> <div class="post-content"> <p>Clark and co-workers have examined small fullerene clusters for their ability to capture electrons.<a href="#fullereneDimer"><sup>1</sup></a> They first looked at the fullerene dimer, comparing the electron affinity of the dimer having a C-C bond between the two cages (about 1.6-1.7 Å between the two cages) <b>1</b> and where the two cages are interacting only through van der Waals attractions (around 2.6 Å) <b>2</b>. The structures and their radical anions were computed at RI-BP86/TZV. The structures of the two radical anions are shown in Figure 1. Interestingly, the radical anion of <b>2</b> is actually lower in energy that the radical anion of <b>1</b>. Comparisons with some other methods are discussed, including a CASSPT2(5,4)/ANO-L-VDZ, computation, that support this result.</p> <table align="center" border="0" cellspacing="0" cellpadding="4"> <tr align="center" valign="bottom"> <td> <p></p> <div class="jmol" id="C120BondedRadAn"> <a onclick="return false"><br> <img src="/blog/wp-content/C120BondedRadAn.jpg" onclick="insertJmol('C120BondedRadAn',300,300,'C120BondedRadAn.xyz')"></a> </div> <p><b>1</b></p> </td> <td> <p></p> <div class="jmol" id="C120radAn"> <a onclick="return false"><br> <img src="/blog/wp-content/C120radAn.jpg" onclick="insertJmol('C120radAn',300,300,'C120radAn.xyz')"></a> </div> <p><b>2</b></p> </td> </tr> <tr align="center" valign="bottom"> <td> <p></p> <div class="jmol" id="C180radAn"> <a onclick="return false"><br> <img src="/blog/wp-content/C180radAn.jpg" onclick="insertJmol('C180radAn',300,300,'C180radAn.xyz')"></a> </div> <p><b>3</b></p> </td> <td> <p></p> <div class="jmol" id="C240radAn"> <a onclick="return false"><br> <img src="/blog/wp-content/C240radAn.jpg" onclick="insertJmol('C240radAn',300,300,'C240radAn.xyz')"></a> </div> <p><b>4</b></p> </td> </tr> </table> <p align="center"><b>Figure 1</b>. RI-BP86/TZV optimized geometries of the radical anions of <b>1-4</b>.<br>(Be sure to click on these images to be able to manipulate these structures in 3-D!)</p> <p>This suggests that the added electron is being held between the cages, in an interstitial region. That suggested looking at the trimer and tetramer structures <b>3</b> and <b>4</b>. The radical anions of these two oligomers are also shown in Figure 1. These oligomers show electron affinities of 1 eV greater than for fullerene itself, along with the ability to stabilize the dianion and even the trianion, what the authors call “deep electron traps”.</p> <h3>References</h3> <p><a name="fullereneDimer"></a></p> <p>(1) Shubina, T. E.; Sharapa, D. I.; Schubert, C.; Zahn, D.; Halik, M.; Keller, P. A.; Pyne, S. G.; Jennepalli, S.; Guldi, D. M.; Clark, T. "Fullerene Van der Waals Oligomers as Electron Traps," <i>J. Am. Chem. Soc.</i> <b>2014</b>, <i>136</i>, 10890-10893, DOI: <a href="http://dx.doi.org/10.1021/ja505949m">10.1021/ja505949m</a>.</p>  </div> <p class="bottom"> <span class="cat"><a href="/blog/archives/category/molecules/fullerene" rel="category tag">fullerene</a></span> <span class="user">Steven Bachrach</span> <span class="date">15 Sep 2014</span> <span class="comments"><a href="/blog/archives/3243#respond">No Comments</a></span> </p> </div> <div class="box"> <h2><a href="/blog/archives/3237" rel="bookmark" title="Permanent Link: Organocatalytic Enantioselective Michael Addition">Organocatalytic Enantioselective Michael Addition</a></h2> <div class="post-content"> <p>Computational techniques are gaining some traction in helping to understand enantioselective organocatalysis. I talk about a few examples in Chapter 6.3 of my book. Lambert and Vetticatt have now used computations to help understand the role of the catalyst <b>4</b> in the Michael addition shown in Scheme 1.<a href="#vetticatt"><sup>1</sup></a> This reaction proceeds with 99% yield and an ee of 98%.</p> <p align="center"><b>Scheme 1.</b></p> <p align="center"><img src="/blog/wp-content/vett_Img.png"></p> <p><sup>13</sup>C kinetic isotope effect studies suggest that the rate determining step is the C-C bond formation (the Michael addition step) which follows the deprotonation of the imine <b>1</b> by the catalyst <b>4</b>.</p> <p>They performed ONIOM computations to search for transition states of this rate limiting step for the reaction in Scheme 1, using the full molecules. From this ONIOM search, the energies for all transition structures with 5 kcal mol<sup>-1</sup> of the lowest energy structure were then obtained at B3LYP/6-31G*. The three lowest energy TS are shown in Figure 1. The two lowest energy structures lead to the major enantiomer, while the third lowest energy structure leads to the minor enantiomer. These energies lead to a prediction of an ee of 92%, in reasonable agreement with the experiment. The computed kinetic isotope effects are in nice agreement with experiment, supporting this step as the overall rate limiting step.</p> <table align="center" border="0" cellspacing="0" cellpadding="3"> <tr align="center"> <td colspan="2"> <p>TSs leading to the <i>S</i> isomer</p> </td> </tr> <tr align="center"> <td> <p></p> <div class="jmol" id="vett_TS1"> <a onclick="return false"><br> <img src="/blog/wp-content/vett_TS1.png" onclick="insertJmol('vett_TS1',300,300,'vett_TS1.xyz')"></a> </div> <p><b>TS1</b><br>(0.0)</p> </td> <td> <p></p> <div class="jmol" id="vett_TS2"> <a onclick="return false"><br> <img src="/blog/wp-content/vett_TS2.png" onclick="insertJmol('vett_TS2',300,300,'vett_TS2.xyz')"></a> </div> <p><b>TS2</b><br>(0.9)</p> </td> </tr> <tr align="center"> <td colspan="2"> <p>TS leading to the <i>R</i> isomer</p> </td> </tr> <tr align="center"> <td colspan="2"> <p></p> <div class="jmol" id="vett_TS3"> <a onclick="return false"><br> <img src="/blog/wp-content/vett_TS3.png" onclick="insertJmol('vett_TS3',300,300,'vett_TS3.xyz')"></a> </div> <p><b>TS3</b><br>(1.7)</p> </td> </tr> </table> <p><b>Table 1</b>. ONIOM optimized geometries of the three lowest energy TSs. Relative energy (kcal mol<sup>-1</sup>) in parenthesis. </p> <p>Analysis of what factors are important in determining the ee is complicated and ultimately the authors are unable to provide a simple explanation. They properly note that</p> <blockquote><p>The observation that the major enantiomer (<i>S</i>) is formed from two very geometrically distinct transition structures … suggests that the prediction of enantioselectivity for other reactions … will require a full consideration of <b>all possible transition state assemblies.</b> <i>(emphasis mine)</i></p></blockquote> <p>I agree with this sentiment, pessimistic as it may be. Answering this type of question is likely to remain very challenging for years to come.</p> <h3>References</h3> <p><a name="vetticatt"></a></p> <p>1) Bandar, J. S.; Sauer, G. S.; Wulff, W. D.; Lambert, T. H.; Vetticatt, M. J. "Transition State Analysis of Enantioselective Brønsted Base Catalysis Chiral Cyclopropenimines," <i>J. Am. Chem. Soc.</i> <b>2014</b>, <i>136</i>, 10700-10707, DOI: <a href="http://dx.doi.org/10.1021/ja504532d">10.1021/ja504532d</a>.</p> <h3>InChIs</h3> <p><b>1</b>: InChI=1S/C20H23NO/c1-20(2,3)14-18(22)15-21-19(16-10-6-4-7-11-16)17-12-8-5-9-13-17/h4-13H,14-15H2,1-3H3<br>InChIKey=UZCWUGCTNCNJHI-UHFFFAOYSA-N</p> <p><b>2</b>: InChI=1S/C4H6O2/c1-3-4(5)6-2/h3H,1H2,2H3<br>InChIKey=BAPJBEWLBFYGME-UHFFFAOYSA-N</p> <p><b>3</b>: InChI=1S/C24H29NO3/c1-24(2,3)17-21(26)20(15-16-22(27)28-4)25-23(18-11-7-5-8-12-18)19-13-9-6-10-14-19/h5-14,20H,15-17H2,1-4H3/t20-/m0/s1<br>InChIKey=KTASCPHNNZODSX-FQEVSTJZSA-N</p> <p><b>4</b>: InChI=1S/C37H57N3/c1-2-30(28-29-18-8-3-9-19-29)38-35-36(39(31-20-10-4-11-21-31)32-22-12-5-13-23-32)37(35)40(33-24-14-6-15-25-33)34-26-16-7-17-27-34/h3,8-9,18-19,30-34H,2,4-7,10-17,20-28H2,1H3/t30-/m1/s1<br>InChIKey=GEHSIGXXLTVFFG-SSEXGKCCSA-N</p>  </div> <p class="bottom"> <span class="cat"><a href="/blog/archives/category/reactions/michael-addition" rel="category tag">Michael addition</a></span> <span class="user">Steven Bachrach</span> <span class="date">08 Sep 2014</span> <span class="comments"><a href="/blog/archives/3237#respond">No Comments</a></span> </p> </div> <div class="box"> <h2><a href="/blog/archives/3221" rel="bookmark" title="Permanent Link: 18π-electron tautomers">18π-electron tautomers</a></h2> <div class="post-content"> <p>Muranaka and Uchiyama have prepared an 18π-electron system that exhibits variable aromaticity in its tautomeric forms.<a href="#Benz18pi"><sup>1</sup></a> The synthesized benziphthalacyanine <b>1</b> shows upfield resonances in the <sup>1</sup>H NMR for the internal hydrogens: 1.89 ppm for the C-H proton and 4.67 ppm for the N-H proton. This indicates some weak diatropicity.</p> <p align="center"><img src="/blog/wp-content/Benz18img1.png"></p> <p>To address this interesting magnetic property, they reported B3LYP/6-31+G(d) computations on the model system <b>2</b> in its phenol <b>2p</b> and quinoidal <b>2q</b> tautomeric forms.</p> <p align="center"><img src="/blog/wp-content/Benz18Img2.png"></p> <p>The optimized structures are shown in Figure 1. The phenol form <b>2p</b> has NICS(0) and NICS(1) values of -6.77 and -6.04 ppm, respectively, indicating only modest aromaticity. However, the NICS values for the quinoidal from <b>2q</b> are much more negative, -11.43 (NICS(0)) and -10.10 (NICS(1)) ppm, indicating a more significant aromatic character. The calculated chemical shift of the internal C-H is most telling: for <b>2q</b> it is -4.55ppm but for <b>2p</b> it is 0.97 ppm, in good agreement with experiment. Thus, <b>1</b> has an 18π-electron modestly aromatic periphery, with the phenol form dominant. There is no evidence of a 20π-electron periphery.</p> <table align="center" border="0" cellspacing="0" cellpadding="3"> <tr align="center"> <td> <p></p> <div class="jmol" id="Benz18P"> <a onclick="return false"><br> <img src="/blog/wp-content/Benz18P.jpg" onclick="insertJmol('Benz18P',300,300,'Benz18P.xyz')"></a> </div> <p><b>2p</b></p> </td> <td> <p></p> <div class="jmol" id="Benz18Q"> <a onclick="return false"><br> <img src="/blog/wp-content/Benz18Q.jpg" onclick="insertJmol('Benz18Q',300,300,'Benz18Q.xyz')"></a> </div> <p><b>2q</b></p> </td> </tr> </table> <p align="center"><b>Figure 1.</b> B3LYP/6-31+G(d) optimized geometries of <b>2p</b> and <b>2q</b>.</p> <p>(Note that the supporting materials have a missing carbon in <b>2q</b> and I have made a guess at its proper location – so this is not quite the optimized structure! Once again, a statement about the quality of SI!)</p> <h3>References</h3> <p><a name="Benz18pi"></a></p> <p>(1) Toriumi, N.; Muranaka, A.; Hirano, K.; Yoshida, K.; Hashizume, D.; Uchiyama, M. "18π-Electron Tautomeric Benziphthalocyanine: A Functional Near-Infrared Dye with Tunable Aromaticity," <i>Angew. Chem. Int. Ed.</i> <b>2014</b>, <i>53</i>, 7814-7818, DOI: <a href="http://dx.doi.org/10.1002/anie.201404020">10.1002/anie.201404020</a>.</p> <h3>InChIs</h3> <p><b>1</b>: InChI=1S/C108H125N7O2/c1-57(2)75-31-25-32-76(58(3)4)87(75)43-69-49-93-95(51-71(69)45-89-79(61(9)10)35-27-36-80(89)62(11)12)105-111-103(93)109-99-55-100(102(117)56-101(99)116)110-104-94-50-70(44-88-77(59(5)6)33-26-34-78(88)60(7)8)72(46-90-81(63(13)14)37-28-38-82(90)64(15)16)52-96(94)106(112-104)114-108-98-54-74(48-92-85(67(21)22)41-30-42-86(92)68(23)24)73(53-97(98)107(113-105)115-108)47-91-83(65(17)18)39-29-40-84(91)66(19)20/h25-42,49-68,116-117H,43-48H2,1-24H3,(H,109,110,111,112,113,114,115)<br>InChIKey=LCYQUXHUTZWPDZ-UHFFFAOYSA-N</p> <p><b>2p</b>: InChI=1S/C30H17N7O2/c38-23-14-24(39)22-13-21(23)31-25-15-7-1-3-9-17(15)27(33-25)35-29-19-11-5-6-12-20(19)30(37-29)36-28-18-10-4-2-8-16(18)26(32-22)34-28/h1-14,38-39H,(H,31,32,33,34,35,36,37)<br>InChIKey=JBKUPBCBFUTSRM-UHFFFAOYSA-N</p> <p><b>2q</b>: InChI=1S/C30H17N7O2/c38-23-14-24(39)22-13-21(23)31-25-15-7-1-3-9-17(15)27(33-25)35-29-19-11-5-6-12-20(19)30(37-29)36-28-18-10-4-2-8-16(18)26(32-22)34-28/h1-14H,(H3,31,32,33,34,35,36,37,38,39)<br>InChIKey=PSSSGMKTDQVWLR-UHFFFAOYSA-N</p>  </div> <p class="bottom"> <span class="cat"><a href="/blog/archives/category/aromaticity" rel="category tag">Aromaticity</a></span> <span class="user">Steven Bachrach</span> <span class="date">02 Sep 2014</span> <span class="comments"><a href="/blog/archives/3221#respond">No Comments</a></span> </p> </div> <p align="center"></p> </div> <div id="sidebar"> <ul> <li class="box"> <h2> Categories </h2> <ul> <li class="cat-item cat-item-25"> <a href="/blog/archives/category/acidity">Acidity</a> (12) </li> <li class="cat-item cat-item-3"> <a href="/blog/archives/category/aromaticity">Aromaticity</a> (91) </li> <li class="cat-item cat-item-53"> <a href="/blog/archives/category/authors">Authors</a> (153) <ul class="children"> <li class="cat-item cat-item-42"> <a href="/blog/archives/category/authors/borden">Borden</a> (12) </li> <li class="cat-item cat-item-12"> <a href="/blog/archives/category/authors/cramer">Cramer</a> (11) </li> <li class="cat-item cat-item-83"> <a href="/blog/archives/category/authors/grimme">Grimme</a> (17) </li> <li class="cat-item cat-item-9"> <a href="/blog/archives/category/authors/houk">Houk</a> (40) </li> <li class="cat-item cat-item-29"> <a href="/blog/archives/category/authors/jorgensen">Jorgensen</a> (3) </li> <li class="cat-item cat-item-16"> <a href="/blog/archives/category/authors/kass">Kass</a> (9) </li> <li class="cat-item cat-item-30"> <a href="/blog/archives/category/authors/schaefer">Schaefer</a> (13) </li> <li class="cat-item cat-item-17"> <a href="/blog/archives/category/authors/schleyer">Schleyer</a> (24) </li> <li class="cat-item cat-item-73"> <a href="/blog/archives/category/authors/schreiner">Schreiner</a> (29) </li> <li class="cat-item cat-item-6"> <a href="/blog/archives/category/authors/singleton">Singleton</a> (11) </li> <li class="cat-item cat-item-18"> <a href="/blog/archives/category/authors/truhlar">Truhlar</a> (8) </li> </ul> </li> <li class="cat-item cat-item-15"> <a href="/blog/archives/category/bond-dissociation-energy">Bond Dissociation Energy</a> (6) </li> <li class="cat-item cat-item-81"> <a href="/blog/archives/category/bsse">BSSE</a> (1) </li> <li class="cat-item cat-item-88"> <a href="/blog/archives/category/cyclophane">cyclophane</a> (0) </li> <li class="cat-item cat-item-4"> <a href="/blog/archives/category/dynamics">Dynamics</a> (35) </li> <li class="cat-item cat-item-57"> <a href="/blog/archives/category/e-publishing">E-publishing</a> (7) </li> <li class="cat-item cat-item-65"> <a href="/blog/archives/category/enzyme">Enzyme</a> (4) </li> <li class="cat-item cat-item-95"> <a href="/blog/archives/category/fep">FEP</a> (1) </li> <li class="cat-item cat-item-86"> <a href="/blog/archives/category/host-guest">host-guest</a> (6) </li> <li class="cat-item cat-item-84"> <a href="/blog/archives/category/hydrogen-bond">Hydrogen bond</a> (5) </li> <li class="cat-item cat-item-91"> <a href="/blog/archives/category/ion-pairs">Ion Pairs</a> (1) </li> <li class="cat-item cat-item-74"> <a href="/blog/archives/category/isotope-effects">Isotope Effects</a> (5) </li> <li class="cat-item cat-item-67"> <a href="/blog/archives/category/keto-enol-tautomerization">Keto-enol tautomerization</a> (3) </li> <li class="cat-item cat-item-54"> <a href="/blog/archives/category/molecules">Molecules</a> (100) <ul class="children"> <li class="cat-item cat-item-48"> <a href="/blog/archives/category/molecules/adamantane">adamantane</a> (3) </li> <li class="cat-item cat-item-26"> <a href="/blog/archives/category/molecules/amino-acids">amino acids</a> (13) </li> <li class="cat-item cat-item-19"> <a href="/blog/archives/category/molecules/annulenes">annulenes</a> (8) </li> <li class="cat-item cat-item-27"> <a href="/blog/archives/category/molecules/benzynes">benzynes</a> (4) </li> <li class="cat-item cat-item-46"> <a href="/blog/archives/category/molecules/biphenyl">biphenyl</a> (1) </li> <li class="cat-item cat-item-70"> <a href="/blog/archives/category/molecules/calixarenes">calixarenes</a> (1) </li> <li class="cat-item cat-item-33"> <a href="/blog/archives/category/molecules/carbenes">carbenes</a> (13) </li> <li class="cat-item cat-item-72"> <a href="/blog/archives/category/molecules/cyclobutadiene">cyclobutadiene</a> (4) </li> <li class="cat-item cat-item-62"> <a href="/blog/archives/category/molecules/dendralenes">dendralenes</a> (1) </li> <li class="cat-item cat-item-66"> <a href="/blog/archives/category/molecules/dewar-benzene">Dewar benzene</a> (1) </li> <li class="cat-item cat-item-39"> <a href="/blog/archives/category/molecules/diradicals">diradicals</a> (8) </li> <li class="cat-item cat-item-59"> <a href="/blog/archives/category/molecules/ephedrine">ephedrine</a> (1) </li> <li class="cat-item cat-item-37"> <a href="/blog/archives/category/molecules/ethyl-cation">ethyl cation</a> (2) </li> <li class="cat-item cat-item-90"> <a href="/blog/archives/category/molecules/fullerene">fullerene</a> (6) </li> <li class="cat-item cat-item-51"> <a href="/blog/archives/category/molecules/fulvalenes">fulvalenes</a> (1) </li> <li class="cat-item cat-item-21"> <a href="/blog/archives/category/molecules/hexacyclinol">hexacyclinol</a> (2) </li> <li class="cat-item cat-item-78"> <a href="/blog/archives/category/molecules/nanohoops">nanohoops</a> (4) </li> <li class="cat-item cat-item-41"> <a href="/blog/archives/category/molecules/non-classical">non-classical</a> (4) </li> <li class="cat-item cat-item-34"> <a href="/blog/archives/category/molecules/norbornyl-cation">norbornyl cation</a> (2) </li> <li class="cat-item cat-item-49"> <a href="/blog/archives/category/molecules/nucleic-acids">nucleic acids</a> (4) </li> <li class="cat-item cat-item-36"> <a href="/blog/archives/category/molecules/oximes">oximes</a> (1) </li> <li class="cat-item cat-item-75"> <a href="/blog/archives/category/molecules/phenyloxenium">phenyloxenium</a> (1) </li> <li class="cat-item cat-item-8"> <a href="/blog/archives/category/molecules/polycyclic-aromatics">polycyclic aromatics</a> (7) </li> <li class="cat-item cat-item-50"> <a href="/blog/archives/category/molecules/propellane">propellane</a> (2) </li> <li class="cat-item cat-item-79"> <a href="/blog/archives/category/molecules/stilbene">stilbene</a> (1) </li> <li class="cat-item cat-item-80"> <a href="/blog/archives/category/molecules/sugars">sugars</a> (5) </li> <li class="cat-item cat-item-85"> <a href="/blog/archives/category/molecules/terpenes">terpenes</a> (2) </li> <li class="cat-item cat-item-89"> <a href="/blog/archives/category/molecules/twistane">twistane</a> (1) </li> </ul> </li> <li class="cat-item cat-item-22"> <a href="/blog/archives/category/nmr">NMR</a> (40) </li> <li class="cat-item cat-item-31"> <a href="/blog/archives/category/optical-rotation">Optical Rotation</a> (16) </li> <li class="cat-item cat-item-28"> <a href="/blog/archives/category/qm-method">QM Method</a> (96) <ul class="children"> <li class="cat-item cat-item-20"> <a href="/blog/archives/category/qm-method/caspt2">CASPT2</a> (1) </li> <li class="cat-item cat-item-7"> <a href="/blog/archives/category/qm-method/dft">DFT</a> (71) </li> <li class="cat-item cat-item-45"> <a href="/blog/archives/category/qm-method/focal-point">focal point</a> (7) </li> <li class="cat-item cat-item-14"> <a href="/blog/archives/category/qm-method/g3">G3</a> (3) </li> <li class="cat-item cat-item-60"> <a href="/blog/archives/category/qm-method/mp">MP</a> (11) </li> </ul> </li> <li class="cat-item cat-item-56"> <a href="/blog/archives/category/reactions">Reactions</a> (83) <ul class="children"> <li class="cat-item cat-item-13"> <a href="/blog/archives/category/reactions/12-addition">1,2-addition</a> (1) </li> <li class="cat-item cat-item-35"> <a href="/blog/archives/category/reactions/aldol">aldol</a> (4) </li> <li class="cat-item cat-item-32"> <a href="/blog/archives/category/reactions/bergman-cyclization">Bergman cyclization</a> (6) </li> <li class="cat-item cat-item-44"> <a href="/blog/archives/category/reactions/claisen-rearrangement">Claisen rearrangement</a> (2) </li> <li class="cat-item cat-item-10"> <a href="/blog/archives/category/reactions/cope-rearrangement">Cope Rearrangement</a> (5) </li> <li class="cat-item cat-item-69"> <a href="/blog/archives/category/reactions/cycloadditions">cycloadditions</a> (12) </li> <li class="cat-item cat-item-23"> <a href="/blog/archives/category/reactions/diels-alder">Diels-Alder</a> (26) </li> <li class="cat-item cat-item-47"> <a href="/blog/archives/category/reactions/electrocyclization">electrocyclization</a> (11) </li> <li class="cat-item cat-item-76"> <a href="/blog/archives/category/reactions/electrophilic-aromatic-substitution">electrophilic aromatic substitution</a> (1) </li> <li class="cat-item cat-item-5"> <a href="/blog/archives/category/reactions/ene-reaction">ene reaction</a> (1) </li> <li class="cat-item cat-item-52"> <a href="/blog/archives/category/reactions/hajos-parrish-reaction">Hajos-Parrish Reaction</a> (1) </li> <li class="cat-item cat-item-61"> <a href="/blog/archives/category/reactions/mannich">Mannich</a> (2) </li> <li class="cat-item cat-item-64"> <a href="/blog/archives/category/reactions/michael-addition">Michael addition</a> (5) </li> <li class="cat-item cat-item-40"> <a href="/blog/archives/category/reactions/ozonolysis">ozonolysis</a> (1) </li> <li class="cat-item cat-item-43"> <a href="/blog/archives/category/reactions/proton-transfer">proton transfer</a> (1) </li> <li class="cat-item cat-item-38"> <a href="/blog/archives/category/reactions/pseudopericyclic">pseudopericyclic</a> (4) </li> <li class="cat-item cat-item-63"> <a href="/blog/archives/category/reactions/strecker">Strecker</a> (1) </li> <li class="cat-item cat-item-24"> <a href="/blog/archives/category/reactions/substitution">Substitution</a> (6) </li> <li class="cat-item cat-item-93"> <a href="/blog/archives/category/reactions/wittig">Wittig</a> (1) </li> </ul> </li> <li class="cat-item cat-item-87"> <a href="/blog/archives/category/second-edition">Second Edition</a> (3) </li> <li class="cat-item cat-item-11"> <a href="/blog/archives/category/solvation">Solvation</a> (17) </li> <li class="cat-item cat-item-77"> <a href="/blog/archives/category/stereochemistry">Stereochemistry</a> (2) </li> <li class="cat-item cat-item-68"> <a href="/blog/archives/category/stereoinduction">stereoinduction</a> (4) </li> <li class="cat-item cat-item-71"> <a href="/blog/archives/category/tunneling">Tunneling</a> (26) </li> <li class="cat-item cat-item-1"> <a href="/blog/archives/category/uncategorized">Uncategorized</a> (57) </li> <li class="cat-item cat-item-82"> <a href="/blog/archives/category/vibrational-frequencies">vibrational frequencies</a> (3) </li> </ul> </li> <li class="box"> <h2> Monthly </h2> <ul> <li><a href="/blog/archives/date/2019/06">June 2019</a></li> <li><a href="/blog/archives/date/2019/04">April 2019</a></li> <li><a href="/blog/archives/date/2019/03">March 2019</a></li> <li><a href="/blog/archives/date/2019/02">February 2019</a></li> <li><a href="/blog/archives/date/2019/01">January 2019</a></li> <li><a href="/blog/archives/date/2018/12">December 2018</a></li> <li><a href="/blog/archives/date/2018/11">November 2018</a></li> <li><a href="/blog/archives/date/2018/10">October 2018</a></li> <li><a href="/blog/archives/date/2018/09">September 2018</a></li> <li><a href="/blog/archives/date/2018/08">August 2018</a></li> <li><a href="/blog/archives/date/2018/07">July 2018</a></li> <li><a href="/blog/archives/date/2018/06">June 2018</a></li> <li><a href="/blog/archives/date/2018/05">May 2018</a></li> <li><a href="/blog/archives/date/2018/04">April 2018</a></li> <li><a href="/blog/archives/date/2018/03">March 2018</a></li> <li><a href="/blog/archives/date/2018/02">February 2018</a></li> <li><a href="/blog/archives/date/2018/01">January 2018</a></li> <li><a href="/blog/archives/date/2017/12">December 2017</a></li> <li><a href="/blog/archives/date/2017/11">November 2017</a></li> <li><a href="/blog/archives/date/2017/10">October 2017</a></li> <li><a href="/blog/archives/date/2017/09">September 2017</a></li> <li><a href="/blog/archives/date/2017/08">August 2017</a></li> <li><a href="/blog/archives/date/2017/07">July 2017</a></li> <li><a href="/blog/archives/date/2017/06">June 2017</a></li> <li><a href="/blog/archives/date/2017/05">May 2017</a></li> <li><a href="/blog/archives/date/2017/04">April 2017</a></li> <li><a href="/blog/archives/date/2017/03">March 2017</a></li> <li><a href="/blog/archives/date/2017/02">February 2017</a></li> <li><a href="/blog/archives/date/2017/01">January 2017</a></li> <li><a href="/blog/archives/date/2016/12">December 2016</a></li> <li><a href="/blog/archives/date/2016/11">November 2016</a></li> <li><a href="/blog/archives/date/2016/10">October 2016</a></li> <li><a href="/blog/archives/date/2016/09">September 2016</a></li> <li><a href="/blog/archives/date/2016/08">August 2016</a></li> <li><a href="/blog/archives/date/2016/07">July 2016</a></li> <li><a href="/blog/archives/date/2016/06">June 2016</a></li> <li><a href="/blog/archives/date/2016/05">May 2016</a></li> <li><a href="/blog/archives/date/2016/04">April 2016</a></li> <li><a href="/blog/archives/date/2016/03">March 2016</a></li> <li><a href="/blog/archives/date/2016/02">February 2016</a></li> <li><a href="/blog/archives/date/2016/01">January 2016</a></li> <li><a href="/blog/archives/date/2015/12">December 2015</a></li> <li><a href="/blog/archives/date/2015/11">November 2015</a></li> <li><a href="/blog/archives/date/2015/10">October 2015</a></li> <li><a href="/blog/archives/date/2015/09">September 2015</a></li> <li><a href="/blog/archives/date/2015/08">August 2015</a></li> <li><a href="/blog/archives/date/2015/07">July 2015</a></li> <li><a href="/blog/archives/date/2015/06">June 2015</a></li> <li><a href="/blog/archives/date/2015/05">May 2015</a></li> <li><a href="/blog/archives/date/2015/04">April 2015</a></li> <li><a href="/blog/archives/date/2015/03">March 2015</a></li> <li><a href="/blog/archives/date/2015/02">February 2015</a></li> <li><a href="/blog/archives/date/2015/01">January 2015</a></li> <li><a href="/blog/archives/date/2014/12">December 2014</a></li> <li><a href="/blog/archives/date/2014/11">November 2014</a></li> <li><a href="/blog/archives/date/2014/10">October 2014</a></li> <li><a href="/blog/archives/date/2014/09" aria-current="page">September 2014</a></li> <li><a href="/blog/archives/date/2014/08">August 2014</a></li> <li><a href="/blog/archives/date/2014/07">July 2014</a></li> <li><a href="/blog/archives/date/2014/06">June 2014</a></li> <li><a href="/blog/archives/date/2014/05">May 2014</a></li> <li><a href="/blog/archives/date/2014/04">April 2014</a></li> <li><a href="/blog/archives/date/2014/03">March 2014</a></li> <li><a href="/blog/archives/date/2014/02">February 2014</a></li> <li><a href="/blog/archives/date/2014/01">January 2014</a></li> <li><a href="/blog/archives/date/2013/12">December 2013</a></li> <li><a href="/blog/archives/date/2013/11">November 2013</a></li> <li><a href="/blog/archives/date/2013/10">October 2013</a></li> <li><a href="/blog/archives/date/2013/09">September 2013</a></li> <li><a href="/blog/archives/date/2013/08">August 2013</a></li> <li><a href="/blog/archives/date/2013/07">July 2013</a></li> <li><a href="/blog/archives/date/2013/06">June 2013</a></li> <li><a href="/blog/archives/date/2013/05">May 2013</a></li> <li><a href="/blog/archives/date/2013/04">April 2013</a></li> <li><a href="/blog/archives/date/2013/03">March 2013</a></li> <li><a href="/blog/archives/date/2013/02">February 2013</a></li> <li><a href="/blog/archives/date/2013/01">January 2013</a></li> <li><a href="/blog/archives/date/2012/12">December 2012</a></li> <li><a href="/blog/archives/date/2012/11">November 2012</a></li> <li><a href="/blog/archives/date/2012/10">October 2012</a></li> <li><a href="/blog/archives/date/2012/09">September 2012</a></li> <li><a href="/blog/archives/date/2012/08">August 2012</a></li> <li><a href="/blog/archives/date/2012/07">July 2012</a></li> <li><a href="/blog/archives/date/2012/06">June 2012</a></li> <li><a href="/blog/archives/date/2012/05">May 2012</a></li> <li><a href="/blog/archives/date/2012/04">April 2012</a></li> <li><a href="/blog/archives/date/2012/03">March 2012</a></li> <li><a href="/blog/archives/date/2012/02">February 2012</a></li> <li><a href="/blog/archives/date/2012/01">January 2012</a></li> <li><a href="/blog/archives/date/2011/12">December 2011</a></li> <li><a href="/blog/archives/date/2011/11">November 2011</a></li> <li><a href="/blog/archives/date/2011/10">October 2011</a></li> <li><a href="/blog/archives/date/2011/09">September 2011</a></li> <li><a href="/blog/archives/date/2011/08">August 2011</a></li> <li><a href="/blog/archives/date/2011/07">July 2011</a></li> <li><a href="/blog/archives/date/2011/06">June 2011</a></li> <li><a href="/blog/archives/date/2011/05">May 2011</a></li> <li><a href="/blog/archives/date/2011/04">April 2011</a></li> <li><a href="/blog/archives/date/2011/03">March 2011</a></li> <li><a href="/blog/archives/date/2011/02">February 2011</a></li> <li><a href="/blog/archives/date/2011/01">January 2011</a></li> <li><a href="/blog/archives/date/2010/12">December 2010</a></li> <li><a href="/blog/archives/date/2010/11">November 2010</a></li> <li><a href="/blog/archives/date/2010/10">October 2010</a></li> <li><a href="/blog/archives/date/2010/09">September 2010</a></li> <li><a href="/blog/archives/date/2010/08">August 2010</a></li> <li><a href="/blog/archives/date/2010/07">July 2010</a></li> <li><a href="/blog/archives/date/2010/06">June 2010</a></li> <li><a href="/blog/archives/date/2010/05">May 2010</a></li> <li><a href="/blog/archives/date/2010/04">April 2010</a></li> <li><a href="/blog/archives/date/2010/03">March 2010</a></li> <li><a href="/blog/archives/date/2010/02">February 2010</a></li> <li><a href="/blog/archives/date/2010/01">January 2010</a></li> <li><a href="/blog/archives/date/2009/12">December 2009</a></li> <li><a href="/blog/archives/date/2009/11">November 2009</a></li> <li><a href="/blog/archives/date/2009/10">October 2009</a></li> <li><a href="/blog/archives/date/2009/09">September 2009</a></li> <li><a href="/blog/archives/date/2009/08">August 2009</a></li> <li><a href="/blog/archives/date/2009/07">July 2009</a></li> <li><a href="/blog/archives/date/2009/06">June 2009</a></li> <li><a href="/blog/archives/date/2009/05">May 2009</a></li> <li><a href="/blog/archives/date/2009/04">April 2009</a></li> <li><a href="/blog/archives/date/2009/03">March 2009</a></li> <li><a href="/blog/archives/date/2009/02">February 2009</a></li> <li><a href="/blog/archives/date/2009/01">January 2009</a></li> <li><a href="/blog/archives/date/2008/12">December 2008</a></li> <li><a href="/blog/archives/date/2008/11">November 2008</a></li> <li><a href="/blog/archives/date/2008/10">October 2008</a></li> <li><a href="/blog/archives/date/2008/09">September 2008</a></li> <li><a href="/blog/archives/date/2008/08">August 2008</a></li> <li><a href="/blog/archives/date/2008/07">July 2008</a></li> <li><a href="/blog/archives/date/2008/06">June 2008</a></li> <li><a href="/blog/archives/date/2008/05">May 2008</a></li> <li><a href="/blog/archives/date/2008/04">April 2008</a></li> <li><a href="/blog/archives/date/2008/03">March 2008</a></li> <li><a href="/blog/archives/date/2008/02">February 2008</a></li> <li><a href="/blog/archives/date/2008/01">January 2008</a></li> <li><a href="/blog/archives/date/2007/12">December 2007</a></li> <li><a href="/blog/archives/date/2007/11">November 2007</a></li> <li><a href="/blog/archives/date/2007/10">October 2007</a></li> <li><a href="/blog/archives/date/2007/09">September 2007</a></li> <li><a href="/blog/archives/date/2007/08">August 2007</a></li> <li><a href="/blog/archives/date/2007/07">July 2007</a></li> </ul> </li> </ul> <a rel="license" href="https://creativecommons.org/licenses/by-nd/3.0/"> <img alt="Creative Commons License" style="border-width:0" src="https://i.creativecommons.org/l/by-nd/3.0/88x31.png"> </a> <br>This work is licensed under a <a rel="license" href="https://creativecommons.org/licenses/by-nd/3.0/">Creative Commons Attribution-No Derivative Works 3.0 Unported License</a>. </div>  <div class="clear"></div> </div>  <div id="footer"> <p>Copyright © 2021 <strong>Computational Organic Chemistry</strong>. </p> </div> </body> </html>