title: Interplay of Nitrogen-Atom Inversion and Conformational Inversion in Enantiomerization of 1H-1-Benzazepines.
abstract: A series of 2,4-disubstituted 1H-1-benzazepines, 2a-d, 4, and 6, were studied, varying both the substituents at C2 and C4 and at the nitrogen atom. The conformational inversion (ring-flip) and nitrogen-atom inversion (N-inversion) energetics were studied by variable-temperature NMR spectroscopy and computations. The steric bulk of the nitrogen-atom substituent was found to affect both the conformation of the azepine ring and the geometry around the nitrogen atom. Also affected were the Gibbs free energy barriers for the ring-flip and the N-inversion. When the nitrogen-atom substituent was alkyl, as in 2a-c, the geometry of the nitrogen atom was nearly planar and the azepine ring was highly puckered; the result was a relatively high-energy barrier to ring-flip and a low barrier to N-inversion. Conversely, when the nitrogen-atom substituent was a hydrogen atom, as in 2d, 4, and 6, the nitrogen atom was significantly pyramidalized and the azepine ring was less puckered; the result here was a relatively high energy barrier to N-inversion and a low barrier to ring-flip. In these N-unsubstituted compounds, it was found computationally that the lowest-energy stereodynamic process was ring-flip coupled with N-inversion, as N-inversion alone had a much higher energy barrier.
authors.affiliation: Department of Natural Sciences, Baruch College of the City University of New York , 17 Lexington Avenue, New York, New York 10010, United States.
authors.forename: Keith
authors.initials: K
authors.lastname: Ramig
authors.affiliation: Department of Chemistry and Biochemistry, Queens College of the City University of New York , 65-30 Kissena Boulevard, Flushing, New York 11367, United States.
authors.forename: Gopal
authors.initials: G
authors.lastname: Subramaniam
authors.affiliation: Department of Chemistry, Queensborough Community College of the City University of New York , 222-05 56th Avenue, Bayside, New York 11364, United States.
authors.forename: Sasan
authors.initials: S
authors.lastname: Karimi
authors.affiliation: Department of Natural Sciences, Baruch College of the City University of New York , 17 Lexington Avenue, New York, New York 10010, United States.
authors.forename: David J
authors.initials: DJ
authors.lastname: Szalda
authors.affiliation: Department of Natural Sciences, Baruch College of the City University of New York , 17 Lexington Avenue, New York, New York 10010, United States.
authors.forename: Allen
authors.initials: A
authors.lastname: Ko
authors.affiliation: Department of Natural Sciences, Baruch College of the City University of New York , 17 Lexington Avenue, New York, New York 10010, United States.
authors.forename: Aaron
authors.initials: A
authors.lastname: Lam
authors.affiliation: Department of Natural Sciences, Baruch College of the City University of New York , 17 Lexington Avenue, New York, New York 10010, United States.
authors.forename: Jeffrey
authors.initials: J
authors.lastname: Li
authors.affiliation: Department of Natural Sciences, Baruch College of the City University of New York , 17 Lexington Avenue, New York, New York 10010, United States.
authors.forename: Ani
authors.initials: A
authors.lastname: Coaderaj
authors.affiliation: Department of Natural Sciences, Baruch College of the City University of New York , 17 Lexington Avenue, New York, New York 10010, United States.
authors.forename: Leyla
authors.initials: L
authors.lastname: Cavdar
authors.affiliation: Department of Natural Sciences, Baruch College of the City University of New York , 17 Lexington Avenue, New York, New York 10010, United States.
authors.forename: Lukasz
authors.initials: L
authors.lastname: Bogdan
authors.affiliation: Department of Natural Sciences, Baruch College of the City University of New York , 17 Lexington Avenue, New York, New York 10010, United States.
authors.forename: Kitae
authors.initials: K
authors.lastname: Kwon
authors.affiliation: Department of Natural Sciences, Baruch College of the City University of New York , 17 Lexington Avenue, New York, New York 10010, United States.
authors.forename: Edyta M
authors.initials: EM
authors.lastname: Greer