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Protonation of some cyclopropylarenes in the gas phase
Author(s) -
Galli Carlo,
Speranza Maurizio
Publication year - 1989
Publication title -
organic mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.475
H-Index - 121
eISSN - 1096-9888
pISSN - 0030-493X
DOI - 10.1002/oms.1210240214
Subject(s) - protonation , steric effects , chemistry , double bond , methyl group , ion cyclotron resonance , fourier transform ion cyclotron resonance , gas phase , ring (chemistry) , stereochemistry , crystallography , group (periodic table) , ion , computational chemistry , organic chemistry , cyclotron
The capability of the cyclopropyl group to conjugate with Unsaturated systems or to delocalize an adjacent positive charge is compared with that of a double bond, and is tested by the determination of the gas‐phase basicity (GB) of various methyl‐substituted cyclopropylbenzenes, α‐methyl styrenes, and biphenyls by Fourier‐transform ion cyclotron resonance. The site of the gas‐phase protonation in the cyclopropylbenzene is established at the three‐membered ring, based on analogy with the trends of GBs in the styrene system upon methyl substitution at the aromatic meta and para positions. The diverse nature of the conjugative interaction of a cyclopropyl group and of a double bond toward an aromatic ring is manifested, instead, in the different behaviour toward a steric perturbation. The cyclopropyl group adopts the bisected conformation in cyclopropylbenzene, because it tolerates the steric perturbation of a methyl group, intentionally placed in the ortho position, more easily than the double bond, which adopts a coplanar conformation in the isomeric α‐methyl styrene.