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Strained Aromatic Compounds: Are σ‐ and π‐Strains Additive? A Hybrid DFT Study of Dicyclobutano‐, Dicyclobutadieno‐ and Di(1,3‐methanocyclopentano)[2,2]paracyclophanes
Author(s) -
Stanger Am,
BenMergui Na'ama,
Perl Sharon
Publication year - 2003
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.200300104
Subject(s) - chemistry , moiety , steric effects , substituent , cyclophane , stereochemistry , aromaticity , crystallography , density functional theory , computational chemistry , molecule , crystal structure , organic chemistry
The structures and energies of dicyclobutano[2,2]paracyclophane ( 1 ), dicyclobutadieno[2,2]paracyclophane ( 2 ) and di(1,3‐methanocyclopentano)[2,2]paracyclophane ( 3 ) were calculated at the B3LYP/6‐31G* theoretical level, in order to understand the behavior of systems that are π‐ and σ‐strained. It was found that the effect of the two types of strain on the geometry is approximately additive, and that the slight deviation found is due to specific interactions (electronic or steric) between the ethano bridges in the [2,2]paracyclophanes and the aromatic moieties or between a substituent and another aromatic moiety. It was found that 1 is ca. 3 kcal mol −1 less strained than [2,2]paracyclophane and cyclobutabenzene, 2 is ca. 6 kcal mol −1 less strained than [2,2]paracyclophane and benzocyclobutadiene, and 3 is ca. 6 kcal mol −1 more strained than [2,2]paracyclophane and 1,3‐methanoindane. These deviations from additivity are explained by the above‐mentioned interactions. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)