Comments on: Are close H…H contacts bonds? The dénouement!

By: The conformation of acetaldehyde: a simple molecule, a complex explanation? « Henry Rzepa

Fri, 08 Feb 2013 16:39:42 +0000

[...] from two C-H bonds (R=H above) into the π*C=O NBO orbital (in the manner that was used to explain the cis-orientation of the two methyl groups in [...]

By: σ-π-Conjugation: seeking evidence by a survey of crystal structures. « Henry Rzepa

Sun, 03 Feb 2013 09:04:52 +0000

[...] molecules are shown above; in effect propene 1 and butene 2. The latter was in fact the topic of another post, in which I attempted to show that the close H…H contact in cis-butene (2.1Å) was in effect [...]

By: A conflation of concepts: Conformation and pericyclic. « Henry Rzepa

A conflation of concepts: Conformation and pericyclic. « Henry Rzepa — Thu, 10 Jan 2013 11:18:37 +0000

[...] In the range IRC ± (9 – 15), unexpected features appear (hidden intermediates if you check this post). A whole plethora of them. This is the conformational region where the methyl flags start waving (and no bonds are formed or broken). If you watch the animation above very carefully, you will note that the methyl groups start rotating at the start and at the end of the migration, at a stage when the ring has an allyl cation. This delocalised cation has a different impact upon the conformation of the methyl groups from that of the transition state, where the charge now resides largely on the migrating carbon, and the ring now has just a neutral butadiene. This latter imparts a different conformational preference upon the methyl groups. You can see an orbital analysis of these effects at this post. [...]

By: π-hydrogen bonds as a function of ring size. « Henry Rzepa

π-hydrogen bonds as a function of ring size. « Henry Rzepa — Sat, 05 Jan 2013 20:30:32 +0000

[...] the scaffold results in a greater overlap of the C=C π and H-O σ* NBOs. Recollect however the H…H distance in cis-butene, a proximity that was enforced by other effects and which I argued was NOT a chemical [...]

By: How is the bromination of alkenes best represented? « Henry Rzepa

How is the bromination of alkenes best represented? « Henry Rzepa — Sun, 14 Oct 2012 21:46:29 +0000

[...] I have pointed out elsewhere that the existence of such a topological feature does not necessarily coincide with what we think [...]

By: A modern take on pericyclic cycloaddition. Dimerisation of cis-butene « Henry Rzepa

Mon, 28 Nov 2011 15:18:44 +0000

[...] and moreover the active space orbitals are probably not identical either (I demonstrated in another post how the orbitals of the alkene interact with those of the methyl groups, and its quite likely that [...]

By: cis-Butene: a reaction coordinate dissected. « Henry Rzepa

cis-Butene: a reaction coordinate dissected. « Henry Rzepa — Wed, 12 Oct 2011 08:16:25 +0000

[...] Henry Rzepa Chemistry with a twist « Are close H…H contacts bonds? The denouement! [...]

By: Are close H…H contacts bonds? « Henry Rzepa

Are close H…H contacts bonds? « Henry Rzepa — Mon, 10 Oct 2011 15:39:07 +0000

[...] Well, not quite. A chemist would still ask why structure (a) is preferred over structure (b), if the wider H…H region is not deemed attractive (I call it a region rather than a bond in a probably futile attempt to avoid controversy). Actually, the answer might be in how the two methyl groups each interact with the other part of the molecule, the alkene, and how that might depend on their orientation with respect to the alkene. But that analysis is for another post! [...]