A new force field has been developed for alkanes and cycloalkanes, excluding small rings, to improve the calculation of vibrational frequencies, rotational barriers, and numerous relatively small errors that were observed to result from the use of the MM3 force field. © 1996 by John Wiley & Sons, Inc.

An improved force field (MM4) for saturated hydrocarbons

Sterically crowded organic molecules: synthesis, structure and properties

Ab initio molecular orbital calculations have been carried out on over 50 model organic molecules and ions to provide the data necessary in the determination of torsional parameters for a force field involving polypeptides. The rotational energy profiles were obtained at the HF/6-31G*//HF/6-31G* level. The results were supported, in many cases, by full geometry optimizations and with consideration of correlation corrections at the MP2 level. With the exception of the dihedral angle being studied, all of the molecules were fully optimized with C1 symmetry. © 1995 by John Wiley & Sons, Inc.

A comprehensive study of the rotational energy profiles of organic systems by ab initio MO theory, forming a basis for peptide torsional parameters

Infolge sterischer Beschleunigung zerfallt Tetra-tert-butylethan (3,4-Di-tert-butyl-2,2,5,5-tetra-methylhexan, 1) schon bei 141°C homolytisch mit t1/2 = 1 h(ΔH≠ =36.4 ± 0.5 kcal/mol; ΔS≠ = 11.8 ± 1.2 cal/mol·grad) in Di-tert-butylmethyl-Radikale. 1 ist der thermolabilste zur Zeit bekannte Alkankohlenwasserstoff. Die Spannungsenergie fur 1 wurde aus kinetischen und thermochemischen Daten sowie Kraftfeldberechnungen zu ca. 63 kcal/mol abgeleitet. Die Kraftfeldberechnungen ergeben in Ubereinstimmung mit NMR-Spektren(3)gauche-Konformation fur 1 als Energieminimum. Die Bindungslange der zentralen CC-Bindung errechnet sich zu ca. 1.60A, der Bindungswinkel CtCtH zu ca. 97° und der Torsionswinkel HCtCtH zu 101°.



Thermolabile Hydrocarbons, IV: Tetra-tert-butylethane



Due to steric acceleration of bond homolysis tetra-tert-butylethane (3,4-di-tert-butyl-2,2,5,5-tetramethylhexane, 1) decomposes at 141°C with t1/2 = 1 h (ΔH≠ = 36.4 ± 0.5 kcal/mol; ΔS≠ = 11.8 ± 1.2 e.u.) into di-tert-butylmethyl radicals. Accordingly 1 is the most thermolabile alkane hydrocarbon known at present. From the kinetics and from thermochemical data as well as from molecular force field calculations a strain energy of ca. 63 kcal/mol is estimated. In agreement with the NMR spectra(3) the force field calculations result in a gauche conformation as structure of minimal energy for 1. Accordingly the central CC-bond is elongated to ca. 1.60 A, the bond CtCtH is compressed to ca. 97° and the torsional angle HCtCtH is ca. 101°.

Thermolabile Kohlenwasserstoffe, IV: Tetra‐tert‐butylethan

Novel 3-(2-adamantyl)pyrrolidines with potent activity against influenza A virus-identification of aminoadamantane derivatives bearing two pharmacophoric amine groups.

L. Lunazzi

Papers

Conformational studies by dynamic NMR. 7. Stereochemical processes in 2,3-dimethylbutane