Comments on: Longer is stronger.

By: Linking numbers, and twist and writhe components for two extended porphyrins. « Henry Rzepa

Sun, 17 Feb 2013 09:30:16 +0000

[...] of π-electrons in cyclically conjugated systems (such as that in benzene[2]), as noted in this earlier post. Such effects may make the interpretation of bond-alternation in such helical systems more [...]

By: The mechanism of the Birch reduction. Part 1. « Henry Rzepa

The mechanism of the Birch reduction. Part 1. « Henry Rzepa — Sun, 02 Dec 2012 10:02:33 +0000

[...] (1.45 – 1.46Å) and four short bonds (1.39-1.41Å). This could be viewed as the result of a pseudo-Jahn-Teller distortion resulting from placing an electron into one of the degenerate LUMO molecular orbitals of the [...]

By: Chemistry in an attosecond. « Henry Rzepa

Chemistry in an attosecond. « Henry Rzepa — Fri, 04 Nov 2011 09:56:34 +0000

[...] or less to the representation above (the hydrogens also wag a bit). This mode even has a name, the Kekulé mode. But even this is not fast enough for the intent of the diagram above, which describes what the [...]

By: Shorter is higher: the strange case of diberyllium. « Henry Rzepa

Shorter is higher: the strange case of diberyllium. « Henry Rzepa — Fri, 21 Jan 2011 11:36:24 +0000

[...] this (higher energy) state is certainly shorter (a contrast with my item on longer being stronger). The length is now 1.78Å, which is more than 1Å shorter than the original state, despite being ~ [...]

By: (anti)aromaticity avoided: a tutorial example « Henry Rzepa

(anti)aromaticity avoided: a tutorial example « Henry Rzepa — Tue, 07 Dec 2010 21:52:09 +0000

[...] delocalisation, and the 4n+2 (n=0) rule predicts aromaticity. Accordingly, all three C-C distances are the same [...]

By: The strongest bond in the universe! « Henry Rzepa

The strongest bond in the universe! « Henry Rzepa — Sun, 24 Oct 2010 11:41:27 +0000

[...] Firstly, one notes that the N-N distance decreases with mono and then diprotonation, the second protonation having the greater effect. Is shorter stronger? [...]

By: Secrets of a university admissions interviewer « Henry Rzepa

Secrets of a university admissions interviewer « Henry Rzepa — Sun, 19 Sep 2010 11:12:59 +0000

[...] suggests little actual aromaticity. The C-O bond length (1.365Å) is certainly short enough. The Kekulé vibrational mode however is quite low (974 cm-1) compared to benzene, which is ~1310 cm-1 (remember, this mode [...]

By: Looking at bonds in a different way: the Laplacian. « Henry Rzepa

Looking at bonds in a different way: the Laplacian. « Henry Rzepa — Mon, 12 Jul 2010 10:21:35 +0000

[...] the C-C or C-H bonds of ethane) but to keep this blog short, I will move on to (and conclude with) benzene, another iconic [...]

By: Chemistry with a super-twist: A molecular trefoil knot, part 2. « Henry Rzepa

Tue, 01 Jun 2010 12:14:46 +0000

[...] being lower than expected due to the phenomenon of π-distortivity (DOI: 10.1039/b911817a and also this post). The mode shown below has the value of 1650 cm-1, which is a good deal higher than for benzene. [...]

By: Chemistry with a super-twist: A molecular trefoil knot. « Henry Rzepa

Chemistry with a super-twist: A molecular trefoil knot. « Henry Rzepa — Mon, 31 May 2010 16:52:53 +0000

[...] to all of the bonds. The origins of this delocalization continue to provoke controversy (see this post). Thus it is thought that only carbon rings with around 24 or less π-electrons can exhibit such [...]

By: Contriving aromaticity from S≡C Triple bonds « Henry Rzepa

Contriving aromaticity from S≡C Triple bonds « Henry Rzepa — Fri, 01 Jan 2010 11:55:16 +0000

[...] (the bottom double-headed arrow). Another way of posing the question is whether the so-called Kekulé vibrational mode (which in effect represents the motions implied above) has a negative force constant or a positive [...]