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The theoretical study of the gas-phase pyrolysis kinetics of several tert -nitroalkanes, 2-methyl-2-nitropropane, 2-methyl-2-nitrobutane, and 2, 3-dimethyl-2-nitrobutane, has been carried out at the MP2/6-31G(d), B3LYP/6-31G(d), B3PW91/6-31G(d), levels of theory. The nitroalkanes yield the corresponding alkene and HNO 2 gas in a rate determining step. The B3PW91/6-31G(d) method was found to give a reasonable good agreement with the experimental kinetic and thermodynamic parameters. The elimination of these reactions suggest a concerted non-synchronous five-membered cyclic transition state type of mechanism.

The gas-phase elimination kinetics of 2-arylethyl N , N -dimethylcarbamates, (CH 3 ) 2 NCOOCH 2 CH 2 Ar, has been studied at the ab initio MP2/6-31G and MPW1PW91/6-31G(d,p) levels of theory. These carbamates produce N , N -dimethylcarbamic acid and the corresponding 4-substituted styrene in a rate determining step. The unstable intermediate N , N -dimethylcarbamic acid rapidly decarboxylate through a four-membered cyclic transition state to give dimethylamine . These calculations imply a concerted, non-synchronous six-membered cyclic transition state type of mechanism. The present results support the fact that the acidity of the benzylic hydrogen as an important factor for faster elimination rates.

The gas-phase elimination of ethyl N,N-dimethylcarbamates substituted with electron-withdrawing groups at the 2-position of the ethyl were studied by using the Moller–Plesset MP2/6-31G method. Calculations suggest a concerted non-synchronous six-membered cyclic transition state type of mechanism of the above-mentioned carbamates. These substrates undergo thermal elimination to produce the N,N-dimethylcarbamic acid and the corresponding substituted olefin in the rate-determining step. The unstable intermediate, N,N-dimethylcarbamic acid rapidly decomposes through a four-membered cyclic transition state to dimethylamine and CO2 gas. The logarithm of relative theoretical rate coefficients when plotted against original Taft's σ* values gave an approximate straight line (ρ*=−0.137±0.023, r=0.9610 at 360 °C). In addition to this fact, plotting experimental log krel. against the theoretical log krel. for 2-substituted ethyl N,N-dimethylcarbamates an approximate straight line (r=0.9578 at 360 °C) is obtained, which means similar mechanism.

The theoretical studies on the elimination kinetics of 2-substituted ethyl N , N -dimethylcarbamates [(CH 3 ) 2 NCOOCH 2 CH 2 Z, Z=CH 2 C 6 H 5 , C 6 H 5 , C(CH 3 ) CH 2 ] in the gas phase were carried out using the ab initio MP2/6-31G and DFT RMPWP91/6-31G(d,p) levels of theory. These carbamates produce N , N -dimethylcarbamic acid and the corresponding substituted olefin in a rate determining step. On the basis of these calculations, the mechanism appears to be concerted, asynchronous, through a six-membered cyclic transition state structure. The acidity of the benzylic and allylic β-hydrogen is believed to be responsible for faster elimination rates.

Moller-Plesset MP2/6-31G method was used to examine the gas-phase elimination of 2-substituted alkyl ethyl N,N-dimethylcarbamates. The results of these calculations support a concerted non-synchronous six-membered cyclic transition state mechanism for carbamates containing a Cβ–H bond at the alkyl side of the ester. These substrates produce the N,N-dimethylcarbamic acid and the corresponding olefin. The unstable intermediate, N,N-dimethylcarbamic acid, rapidly decomposes through a four-membered cyclic transition state to dimethylamine and CO2 gas. Correlation of the logarithm of theoretical rate coefficients against original Taft's σ* values gave an approximate straight line (ρ*=−1.39, r=0.9558 at 360 °C). In addition to this fact, when log krel is plotted against the theoretical log krel for 2-substituted ethyl N,N-dimethylcarbamates a reasonable straight line (r=0.9919 at 360 °C) is obtained, suggesting similar mechanism.

A reliable set of harmonic force constants was calculated for BF 3 , BCl 3 , BBr 3 , BI 3 , BF 2 Cl, BF 2 Br, BCl 2 F, BCl 2 Br, BBr 2 F, and BBr 2 Cl using the observed vibrational frequencies of these compounds (containing 10 B or 11 B isotopes) and the iterative consistency method. The final force field reproduces quite satisfactorily the experimental frequencies. Some of the principal stretching force constants were found to vary systematically with the electronegativity of the halogen.