Talk:Tetraphenylcyclopentadienone

Crystal structures


I think these images more accurately depict the propeller shape of this molecule. Reference is in the description of the image. --Rifleman 82 (talk) 10:14, 19 December 2011 (UTC)

UV spectrum
The absorption of the visible light has nothing to do with "extended conjugation system" as phenyl rings are out of plane of the molecule as can be seen from the X-ray. Anti-aromaticity of this molecule is the reason for a small HOMO-LUMO gap and thus the absorption of light. The formal electron count gives 5 pi electrons in the cyclopentadienone ring what makes this molecule non-aromatic, however since C-O bond is polar, one can envision a contribution from an anti-aromatic 4 pi electron resonance structure too. Two bands around 500 nm and 390 nm are due to electron transfer from HOMO to LUMO (pi->pi*) and from HOMO-1 to LUMO (n->pi*) correspondingly. — Preceding unsigned comment added by Vlp92 (talk • contribs) 21:51, 27 November 2012 (UTC)
 * True enough, but the phenyl rings do affect the spectrum. I don't have the ref handy, but substituting the Ar groups alters the electronic details similar to a simple stilbene. If you have some ideas for clarifying the major intensity feature but also the effects of Ar electronics, please do suggest. I do note that the lead does not say that the phenyls are part of the conjugated system being analyzed, but it does at least imply conjugation from them, which is as you note not correct. DMacks (talk) 21:59, 27 November 2012 (UTC)

Sure, substituents do affect the spectral properties and one can manipulate the absorption maxima wavelength by attaching various groups to the aryl rings. Indeed, the HOMO-1 and HOMO of TPCPD are significantly spread onto aryl groups and hence some conjugation is taking place. But compare it to hexaphenylbenzene, which is a colorless compound! So that, IMHO the major reason for beautiful deep purple color of the TPCPD is its non- and anti-aromatic nature. — Preceding unsigned comment added by 75.128.147.214 (talk) 00:18, 28 November 2012 (UTC)