Conventional strain energy in dimethyl-substituted cyclobutane and the gem-dimethyl effect.
Conventional strain energy in dimethyl-substituted cyclobutane and the gem-dimethyl effect.
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DOI：
10.1021/jo0624647
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发表时间：
2007-03
期刊：
影响因子：
--
通讯作者：
Ashley L. Ringer;D. Magers
中科院分区：
文献类型：
--
作者：
Ashley L. Ringer;D. Magers
The gem-dimethyl effect is the acceleration of cyclization by substituents in the chain and is often used in organic synthesis as a ring-closing effect. Calculations on cyclobutane, methylcyclobutane, and 1,1-dimethylcyclobutane are performed. 1,1-Dimethylcyclobutane is a four-membered carbon ring with gem-dimethyl substituents. Optimum equilibrium geometries, harmonic vibrational frequencies, and corresponding electronic energies are computed for all pertinent molecular systems using SCF theory, density functional theory (DFT), and second-order perturbation theory (MP2) with two triple-zeta quality basis sets, 6-311G(d,p) and 6-311G+(2df,2pd). Additional single-point calculations are performed using the optimized MP2/6-311G+(2df,2pd) geometries and coupled-cluster theory including single and double excitations and noniterative, linear triple excitations (CCSD(T)). Calculations indicate that 1,1-dimethylcyclobutane is more than 8 kcal mol-1 less strained than cyclobutane, that is, there is at least some thermodynamic component to the gem-dimethyl effect.
