Document Detail


Molecular structure and benzene ring deformation of three cyanobenzenes from gas-phase electron diffraction and quantum chemical calculations.
MedLine Citation:
PMID:  18834088     Owner:  NLM     Status:  MEDLINE    
Abstract/OtherAbstract:
The molecular structures of cyanobenzene, p-dicyanobenzene, and 1,2,4,5-tetracyanobenzene have been accurately determined by gas-phase electron diffraction and ab initio/DFT MO calculations. The equilibrium structures of these molecules are planar, but their average geometries in the gaseous phase are nonplanar because of large-amplitude vibrational motions of the substituents out of the plane of the benzene ring. The use of nonplanar models in electron diffraction analysis is necessary to yield ring angles consistent with the results of MO calculations. The angular deformation of the benzene ring in the three molecules is found to be much smaller than obtained from previous electron diffraction studies, as well as from microwave spectroscopy studies of cyanobenzene. While the deformation of the ring CC bonds and CCC angles in p-dicyanobenzene is well interpreted as arising from the superposition of independent effects from each substituent, considerable deviation from additivity occurs in 1,2,4,5-tetracyanobenzene. The changes in the ring geometry and C ipso-C cyano bond lengths in this molecule indicate an enhanced ability of the cyano group to withdraw pi-electrons from the benzene ring, compared with cyanobenzene and p-dicyanobenzene. In particular, gas-phase electron diffraction and MP2 or B3LYP calculations show a small but consistent increase in the mean length of the ring CC bonds for each cyano group and a further increase in 1,2,4,5-tetracyanobenzene. Comparison with accurate results from X-ray and neutron crystallography indicates that in p-dicyanobenzene the internal ring angle at the place of substitution opens slightly as the molecule is frozen in the crystal. The small geometrical change, about 0.6 degrees , is shown to be real and to originate from intermolecular C identical withN...HC interactions in the solid state.
Authors:
Anna Rita Campanelli; Aldo Domenicano; Fabio Ramondo; István Hargittai
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Publication Detail:
Type:  Journal Article     Date:  2008-10-04
Journal Detail:
Title:  The journal of physical chemistry. A     Volume:  112     ISSN:  1520-5215     ISO Abbreviation:  J Phys Chem A     Publication Date:  2008 Oct 
Date Detail:
Created Date:  2008-10-24     Completed Date:  2008-12-17     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  9890903     Medline TA:  J Phys Chem A     Country:  United States    
Other Details:
Languages:  eng     Pagination:  10998-1008     Citation Subset:  IM    
Affiliation:
Department of Chemistry, University of Rome "La Sapienza", I-00185 Rome, Italy.
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MeSH Terms
Descriptor/Qualifier:
Benzene Derivatives / chemistry*
Computer Simulation*
Electrons*
Gases / chemistry
Models, Chemical*
Molecular Structure
Nitriles / chemistry*
Quantum Theory*
Chemical
Reg. No./Substance:
0/1,2,4,5-tetracyanobenzene; 0/Benzene Derivatives; 0/Gases; 0/Nitriles

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine


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