How S–C–N anomeric effects and energetic preference across [S–C–C–O] fragments steer conformational equilibria in 4′-thionucleosides. 1H NMR and ab initio MO study †

2000 ◽  
pp. 255-262 ◽  
Author(s):  
Martin Črnugelj ◽  
David Dukhan ◽  
Jean-Louis Barascut ◽  
Jean-Louis Imbach ◽  
Janez Plavec
Keyword(s):  
Ab Initio ◽  
1H Nmr ◽  
Conformational Equilibria ◽  
Ab Initio Mo ◽  
Anomeric Effects

An ab initio MO study of conformation structure of nicotinamide and its derivatives

1983 ◽  
Vol 48 (7) ◽  
pp. 1842-1853 ◽  
Author(s):  
Stanislav Böhm ◽  
Josef Kuthan
Keyword(s):  
Ab Initio ◽  
Wave Functions ◽  
Semiempirical Calculations ◽  
Rigid Rotor ◽  
Qualitative Similarity ◽  
Ab Initio Mo ◽  
Experimental Findings

Conformation of nicotinamide (I), 3-carbamoylpyridinium (IIa), 1-methyl-3-carbamoylpyridinium (IIb), and 1-methyl-1,4-dihydronicotinamide (IIIa) has been studied in the rigid rotor approximation on the basis of non-empirical STO-3G wave functions. The rotation barriers decrease in the order: IIIa > I ~ IIb > IIa. When confronted with semiempirical calculations, the conformation curves of molecular energy show a better qualitative similarity to the EHT than to NDDO and particularly to CNDO/2 curves. Relation of the calculated characteristics to experimental findings is discussed.

scholarly journals Structural Parameters and Internal Rotational Barriers of tert-Butylammonium Ion: AM1 and ab initio Calculations

1992 ◽  
Vol 47 (12) ◽  
pp. 1255-1256
Author(s):  
Hiroyuki Ishida ◽  
Yoshihiro Kubozono ◽  
Setsuo Kashino ◽  
Ryuichi Ikeda
Keyword(s):  
Ab Initio Calculations ◽  
Ab Initio ◽  
Internal Rotation ◽  
Barrier Height ◽  
Structural Parameters ◽  
Mo Calculations ◽  
Ab Initio Mo Calculations ◽  
Rotational Barriers ◽  
Ab Initio Mo ◽  
Internal Rotational Barriers

Semiempirical and ab initio MO calculations were performed to estimate the structural parameters of tert-butylammonium ion and its potential energies for the internal rotation of the CH3 and NH3+ groups. The barrier height for the rotation of NH3+ was found to be lower than for that of CH3 , corresponding to the C - N bond being longer than the C - C bond.

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