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Motivated by recent experiments on circular dichroism in the photoelectron momentum distributions from strong-field ionization of chiral molecules [C. Lux, Angew. Chem. Int. Ed. 51, 5001 (2012)1433-785110.1002/anie.201109035; C. S. Lehmann, J. Chem. Phys. 139, 234307 (2013)JCPSA60021-960610.1063/1.4844295], we investigate the origin of this effect theoretically. We show that it is not possible to describe photoelectron circular dichroism with the commonly used strong-field approximation due to its plane-wave nature. We therefore apply the Born approximation to the scattering state and use this as a continuum-state correction in the strong-field approximation. We obtain electron distributions for the molecules camphor and fenchone. In order to gain physical insight into the process, we study the contributions of individual molecular orientations. © 2014 American Physical Society.

Received 28 May 2012, Revised 6 September 2012, Accepted 5 October 2012, Available online 13 October 2012., Camphor- and fenchone-based bridgehead-substituted norbornan-2-ones constitute an interesting class of chiral synthons with applications in stereoselective synthesis, due to the wide variety of stereo-controlled transformations which they can undergo. Despite their synthetic value, few mass spectral studies have been realized for these compounds due to the lack of general procedures for their preparation. In this paper we have carried out an electron ionization (EI) mass spectral study of a series of heteroatomically bridgehead-substituted 7,7-dimethylnorbornan-2-ones. Their cleavage mechanisms have been rationalized on the basis of the substituent shifts, as well as on the identification of relevant peaks through accurate mass measurements and collision-induced dissociation (CID) tandem mass-spectrometric experiments. The driving force for the main fragmentation pathways of C(1)-O- and C(1)-N-substituted 7,7-dimethylnorbornan-2-ones is the alpha-cleavage of the C(1) C(2) bond directed by the bridgehead substituent. Further rearrangements and fragmentations of the distonic ions initially formed lead to the major ions in the spectra of all the compounds. A comparison with the known behaviour of their isomeric 3,3-dimethylnorbornan-2-ones reveals that the key bridgehead heteroatom effect controlling the fragmentation pathways can be modulated by the position of the gem-dimethyl group. As a consequence, the corresponding fragmentation patterns of both isomeric series are very different. In contrast, the fragmentation patterns of 7,7-dimethyl-2-oxo-norbornanesulphonamides, whose main fragmentation pathway involves homolytic S N bond cleavage, are almost identical to those displayed by their 3,3-dimethylated isomers, Ministerio de Economía y Competitividad (MINECO), Universidad Complutense de Madrid (España), Depto. de Química Orgánica, Sección Deptal. de Química Orgánica (Óptica y Optometría), Fac. de Ciencias Químicas, Fac. de Óptica y Optometría, TRUE, pub