Conformational Analysis of C60 Ball-and-Chain Molecules: a Molecular Orbital Study

1996 ◽  
Vol 49 (3) ◽  
pp. 395 ◽  
Author(s):  
MJ Shephard ◽  
MN Paddonrow
Keyword(s):  
Conformational Analysis ◽  
Computational Study ◽  
Hydrocarbon Chain ◽  
Am1 Method ◽  
Methyl Groups ◽  
Chain Molecules ◽  
Molecular Orbital Study ◽  
C 30 ◽  
Bichromophoric Molecules ◽  
Conformational Energies

A computational study of the conformational analysis of a series of C60 ball-and-chain bichromophoric molecules (1)-(6) has been carried out by means of the AM1 and HF/3-21G//AM1 theoretical methods. It is found that the AM1 method underestimates both the relative conformational energies and the magnitude of the energy barriers folded and extended conformers. In contrast, the HF/3-21G//AM1 method gives reasonable values for these quantities. The HF/3-21G//AM1 calculated energy differences between the folded and extended conformers of systems (2)-(5) are less than 5 kJ/mol and the barriers to their interconversion are c. 30 kJ/mol. The conformational bias in these systems may be modified by the judicious placement of methyl groups in the region of the hydrocarbon chain closest to the C60 cage. It is found that the length of the chain and the nature of the non-C60. chromophore have little effect on the conformational energetics.

A pairwise additivity scheme for conformational energies of substituted ethanes

1975 ◽  
Vol 343 (1632) ◽  
pp. 1-10 ◽  
Keyword(s):  
Large Deviations ◽  
Ab Initio ◽  
Dihedral Angle ◽  
Molecular Orbital ◽  
Methyl Groups ◽  
Molecular Orbital Calculations ◽  
Linear Combinations ◽  
Strongly Interacting ◽  
Conformational Energies

Ab initio molecular orbital calculations are used to explore additivity in the conformational energies of poly-substituted ethanes in terms of conformational energies of ethane and appropriate mono- and 1,2-di-substituted derivatives. Such relations would allow complex calculations for poly-substituted ethanes to be replaced by much simpler ones on a small number of parent molecules. General expressions for the linear combinations are derived from the assumption that interactions between vicinal substituents are pairwise additive and depend only on the vicinal dihedral angle. The additivity scheme is tested for 15 ethanes, di-, tri- or tetrasubstituted by cyano and methyl groups and for a smaller number of fluoroethanes. Additivity applies to within 0.1- 0.3 k J mol -1 in the methylethanes and mostly to within about 0.7- 0.8 kJ mol -1 in cyanoethanes. Large deviations are found among the geminally substituted fluoroethanes. It is suggested that the additivity approximation is most successful in the absence of strongly interacting geminal groups. Predictions are made of conformational energies of ten hexa(cyano- and methyl-) substituted ethanes.

Conformational analysis of phenylsulphonylalkanoic acids with the AM1 method

1993 ◽  
Vol 283 ◽  
pp. 207-211 ◽  
Author(s):  
Maria Jaworska ◽  
Jarosaw Polański ◽  
Aleksander Ratajczak
Keyword(s):  
Conformational Analysis ◽  
Am1 Method

Conformational features of bisphenol-A polycarbonate

1985 ◽  
Vol 63 (1) ◽  
pp. 103-110 ◽  
Author(s):  
P. R. Sundararajan
Keyword(s):  
Bisphenol A ◽  
Repeat Unit ◽  
Methyl Groups ◽  
Bisphenol A Polycarbonate ◽  
Carbonate Group ◽  
Torsion Angles ◽  
Thermal Crystallization ◽  
Lennard Jones ◽  
Empirical Force Field ◽  
Conformational Energies

Conformational energies have been estimated for the segments of the bisphenol polycarbonate chain, using the Lennard–Jones and Hill's empirical force field type of functions. It is found that the conformation of the carbonate group, defined by the torsion angle ζ, is restricted to the range of 45° to 65°. The rotations χ and χ′ of the methyl groups also show similar limited flexibility. However, accessible conformations of the diphenyl propane (DPP) segment, defined by torsion angles [Formula: see text] and ψ, span a wide area of the [Formula: see text] surface, with the restriction that the rotations [Formula: see text] and ψ be synchronized such that [Formula: see text] or 270°. These features explain the slow thermal crystallization behaviour of the polycarbonate chains. The variability of the conformations of the repeat unit is illustrated with a series of figures.

Conformational analysis of enantiomerization coupled to internal rotation in triptycyl-n-helicenes

2019 ◽  
Vol 21 (21) ◽  
pp. 11395-11404
Author(s):  
Abel Carreras ◽  
Luca Fuligni ◽  
Pere Alemany ◽  
Miquel Llunell ◽  
Josep Maria Bofill ◽  
...  
Keyword(s):  
Potential Energy ◽  
Conformational Analysis ◽  
Potential Energy Surface ◽  
Internal Rotation ◽  
Energy Surface ◽  
Computational Study ◽  
Reaction Coordinate

We present a computational study of a reduced potential energy surface (PES) to describe enantiomerization and internal rotation in three triptycyl-n-helicene molecules, centering the discussion on the issue of a proper reaction coordinate choice.

Rotational tunneling of methyl groups in the hydroquinone/acetonitrile clathrate: A combined deuteron NMR, INS, and computational study

1998 ◽  
Vol 238 (2) ◽  
pp. 301-314 ◽  
Author(s):  
A. Detken ◽  
P. Schiebel ◽  
M.R. Johnson ◽  
H. Zimmermann ◽  
U. Haeberlen
Keyword(s):  
Computational Study ◽  
Methyl Groups ◽  
Deuteron Nmr
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