title: To bend or not to bend! The dilemma of allenes.
abstract: Allenes, though expected to be linear, are found to be bent in many examples, especially in the case of cyclic allenes. The bending of allene is attributed to the weakening of π-bond strength across the allene. However, tetrakis(dimethylamino)allene {((CH(3))N)(2)C═C═C(N(CH(3))(2))}, which is characterized by push-push interactions, has been shown to be linear, thus leading to doubts of the current understanding of the bent allenes. In this article, we report the ab initio MO/DFT, NBO based electronic structure analysis of R(2)C═C═CR(2) (R = H, NH(2)) with a gradual increase in the number of amino substituents. The results indicate that the allenic π-bond strength and bending potential decrease, with an increase in the amino substitution. Molecular orbital analysis provides necessary clues regarding the delicate balance between orthogonality of the π orbitals and the p orbitals on the central carbon, which dictates the bending potential of the allenes. The dilemma of to bend or not to bend is a unique feature of tetraaminoallenes (NH(2))(2)C═C═C(NH(2))(2) in comparison to isoelectronic heteroallenes (NH(2))(2)C═N═C(NH(2))(2)(+) and (NH(2))(2)C═B═C(NH(2))(2)(-).
authors.affiliation: Department of Medicinal Chemistry, National Institute of Pharmaceutical Education and Research, Sector 67, S. A. S. Nagar (Mohali), Punjab 160 062, India.
authors.forename: Dhilon S
authors.initials: DS
authors.lastname: Patel
authors.forename: Prasad V
authors.initials: PV
authors.lastname: Bharatam
mesh_terms: D000466:Alkadienes / Q000737:chemistry*; D000588:Amines / Q000737:chemistry; D002244:Carbon / Q000737:chemistry*; D004583:Electrons; D008958:Models, Molecular; D015394:Molecular Structure; D018583:Pliability
chemical_list: D000466:Alkadienes; D000588:Amines; D002244:Carbon