Applications Atoms_in_molecules

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another molecule studied in qtaim biphenyl. 2 phenyl rings oriented @ 38° angle respect each other planar molecular geometry (encountered in rotation around central c-c bond) destabilized 2.1 kcal/mol (8.8 kj/mol) , perpendicular 1 destabilized 2.5 kcal/mol (10.5 kj/mol). classic explanations rotation barrier steric repulsion between ortho-hydrogen atoms (planar) , breaking of delocalization of pi density on both rings (perpendicular).


in qtaim energy increase on decreasing dihedral angle 38° 0° summation of several factors. destabilizing factors increase in bond length between connecting carbon atoms (because have accommodate approaching hydrogen atoms) , transfer of electronic charge carbon hydrogen. stabilizing factors increased delocalization of pi-electrons 1 ring other , 1 tips balance hydrogen - hydrogen bond between ortho hydrogens.


the hydrogen bond not without critics. according 1 relative stability of phenanthrene compared isomers can adequately explained comparing resonance stabilizations. critic argues stability of phenanthrene can attributed more effective pi-pi overlap in central double bond; existence of bond paths not questioned stabilizing energy derived is.








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