The Alkyl Inductive Effect, II Theoretical Calculation of Inductive Parameters

H a r r y F . W i d i n g a n d L e o n a r d S . L e v i t t Department of Chemistry, College o f Science, The University o f Texas at El Paso, El Paso, Texas 79968 Z. Naturforsch. 34b , 321 -326 (1979) ; received August 29, 1978 Alkyl Induct ive Ef fect , Induct ive Substituent Constants of Alkyl Groups Three models o f alkyl groups, " d e r e a l i z a t i o n " , " throughthe -bond" , and "electric field" models, are presented, all o f which enable the calculation of <7I(R) f r o m first principles, and excellent agreement is demonstrated for the calculated and experimental values o f < 7 i ( R ) . F o r the " d e r e a l i z a t i o n " model it is f ound that — < X I ( R ) = 0.0455 + 0 .0232(1—1/n) , where n is the number o f C atoms in an w-alkyl group, and for an infinite C-chain R group, C R I ( R 0 0 ) is — 0 . 0 6 8 7 , identical to the value found b y a different method in Part I o f this series. The " t h r o u g h t h e b o n d " model gives — F F I ( R ) = — 0 . 0 5 5 9 + ii 0.1015 2 C i / ( 2 i — l ) 2 , where Ci is the number o f C-atoms in the i t h position f r o m X in R X ; 1 n and for the "electric field" mode l , we obtain —CT^R) = 0.0463 + 0.0102 Z C i d r 2 , where di 2 is the calculated distance f r o m Ci to Cn in the most probable conformation o f the R -group . I t is conc luded that Ta f t ' s ( T I ( R ) values have a real significance whether or not the physical and chemical effects o f alkyl substitution reside ultimately in an internal induction mechanism, or in alkyl group polarization b y charged centers in the molecule, or a c ombination o f the two .