Diminished Reactivity of Ortho-Substituted Phenacyl Bromides toward Nucleophilic Displacement

A systematic increase of substitution rates by tert-butylamine on α-bromopropiophenones is observed with meta or para substituents with increasing electron-withdrawing ability (k × 103 L M-1 min-1 = 12.7 (p-CH3), 15.7 (o-F), 20.5 (H), 20.0 (p-Cl), 23.6 (m-Cl), 27.3 (p-CF3)). Within an ortho-substitu...

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Bibliographic Details
Published in:Journal of organic chemistry 2003-02, Vol.68 (4), p.1594-1596
Main Authors: Kalendra, Diane M, Sickles, Barry R
Format: Article
Language:English
Subjects:
Chemistry
Exact sciences and technology
Kinetics and mechanisms
Organic chemistry
Reactivity and mechanisms
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Summary:A systematic increase of substitution rates by tert-butylamine on α-bromopropiophenones is observed with meta or para substituents with increasing electron-withdrawing ability (k × 103 L M-1 min-1 = 12.7 (p-CH3), 15.7 (o-F), 20.5 (H), 20.0 (p-Cl), 23.6 (m-Cl), 27.3 (p-CF3)). Within an ortho-substituted series, the reactivities decrease (k × 103 L M-1 min-1 = 7.64 (o-OCH3), 5.31 (o-CH3), 2.85 (o-Cl), 2.40 ( o-CF3)). Ortho-substitution results occur from rotational barrier effects and an Aδσ + Bδσ + repulsion. The major bonding contribution between reaction and α-substituent centers (A−B) is only the σ bond. When π bonding is allowed between A and B (meta/para-substitution), delocalization and stabilization of the reacting center occurs.
ISSN:0022-3263
1520-6904
DOI:10.1021/jo011042o