Semi-Experimental Equilibrium Structures for Molecules of Biological Significance
EMSL Project ID
24824
Abstract
Polyenes are of great importance in biological chemistry through their roles in vision, in light harvesting in photosynthesis, and in pigmentation. In contrast to the extensive knowledge of the electronic spectroscopy of polyenes, little is known about the impact of pi-electron delocalization on the structure of polyenes. We propose extending our recent work on butadiene, which shows for the first time the subtle effect (changes of 0.01 Å and less) of pi-electron delocalization on structure, to the cis and trans isomers of hexatrienes. It is anticipated that the structural effect of pi-electron delocalization increases with chain length in that "C-C" bonds are shortened more and "C=C" bonds are lengthened more with increasing length of the polyene. Equilibrium structures for the hexatrienes would be derived from ground state rotational constants obtained from the analysis of the extensive rotational structure in high-resolution infrared spectra. Such spectra would be recorded on the Bruker instruments in the Infrared Laboratory at PNNL. In addition, vibration-rotation constants, which would be computed with quantum chemical methods, are needed to extract equilibrium rotational constants from the ground state rotational constants. The equilibrium structure is fitted to the equilibrium rotational constants for a full set of isotopomers, which must be synthesized. A related project involves the impact of fluorine substitution on organic molecules. Because fluorine substituents now play a major role in drug development, having an improved understanding of the relationship between fluorine substitution and consequent electronic effects on the structure of molecules would advance drug discovery. The same methods for obtaining equilibrium structures of the isomers of hexatriene would be applied to the isomers of 1,4-difluorobutadiene. We hypothesize a strong influence of the fluorine substituents on the contiguous C=C bonds and possibly also on the distant C-C bond.
Project Details
Project type
Large-Scale EMSL Research
Start Date
2007-06-01
End Date
2010-09-30
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members
Related Publications
Craig NC, CC Easterday, DJ Nemchick, D Williamson, and RL Sams. 2012. "Rotational Analysis of Bands in the High-Resolution Infrared Spectra of cis,cis- and trans,trans-1,4-difluorobutadiene-2-d1." Journal of Molecular Spectroscopy 272(1):2-10. doi:10.1016/j.jms.2011.11.007
Craig NC, H Tian, and TA Blake. 2012. "Analysis of the Rotational Structure in the High-Resolution Infrared Spectrum of trans-Hexatriene-1-13C1; a Semiexperimental Equilibrium Structure for the C6 Backbone for trans-Hexatriene." Journal of Physical Chemistry A 116(12):3148-3155. doi:10.1021/jp211791r
Craig NC, MC Leyden, MC Moore, AK Patchen, T van den Heuvel, TA Blake, T Masiello, and RL Sams. 2010. "A reevaluation of the assignment of the vibrational fundamentals and the rotational analysis of bands in the high-resolution infrared spectra of trans- and cis- 1,3,5-hexatriene." Journal of Molecular Spectroscopy 262(1):49-60. doi:10.1016/j.jms.2010.05.002
Craig, NC, Moore, MC, Neese, CF, Oertel, DC, Pedraza, L, Masiello, T. 2009. "High-Resolution Infrared Spectra of the Two Nonpolar Isomers of 1,4-Difluorobutadiene." Journal of Molecular Spectroscopy, 254, 39-46.