Stereochemical consequences of halogen-for-halogen substitutions in the gas phase

Stereochemical Consequences of Halogen-for-Halogen Substitutions with Gaseous Enatiomers

“…Previously we studied the stereochemistry of translationally energetic fluorine-for-halogen and chlorine-for-halogen Brought to you by | provisional account Unauthenticated Download Date | 6/29/15 6:50 AM substitution in gaseous chiral 2-halopropionyl halides [19]. We found that the extent of inversion or retention in these energetic substitution reactions appeared to be sensitive to the mass of the incoming atom, to steric hindrance to back-side attack, and to the nature of the halogen leaving group.…”

“…Gas phase substitutions by recoil fluorine [8], chlorine [4,9,10], bromine [2,11], and iodine [11] atoms on substrate molecules containing two chiral centers were also observed to yield high levels of retention. Subsequent studies by this group on gas-phase substitution of 34m Cl on substrate molecules possessing a single chiral center yielded significantly higher levels of inversion [13,19].In stereochemical studies involving high-energy halogen-for-halogen substitution in compounds with single chiral centers, this group [12b, 13,19] reacted recoil 34m Cl, 38 CI, and 18 F atoms, through energetic halogen substitution at the chiral centers of 2-(S)-and 2-(R)-halopropionyl halides, 2-chloro-4-methylvaleryl chloride, and 2-chloro-l-propanol. These studies suggested that hot homolytic substitution (SHH2) reactions at sp 3 -hybridized carbon in the gas phase involving monovalent recoil atoms can occur by either of two reaction channels, one with retention of configuration and the other with inversion of configuration.…”

“…In addition, other factors such as those proposed by ROWLAND [20] for energetic tritium atoms may have importance in the substitution process, namely, bond energy, electronegativity, and electron density. It was suggested that the most critical factor controlling the degree of inversion is the mass of the incoming atom [19]. …”

“…Gas phase substitutions by recoil fluorine [8], chlorine [4,9,10], bromine [2,11], and iodine [11] atoms on substrate molecules containing two chiral centers were also observed to yield high levels of retention. Subsequent studies by this group on gas-phase substitution of 34m Cl on substrate molecules possessing a single chiral center yielded significantly higher levels of inversion [13,19].…”

“…In stereochemical studies involving high-energy halogen-for-halogen substitution in compounds with single chiral centers, this group [12b, 13,19] reacted recoil 34m Cl, 38 CI, and 18 F atoms, through energetic halogen substitution at the chiral centers of 2-(S)-and 2-(R)-halopropionyl halides, 2-chloro-4-methylvaleryl chloride, and 2-chloro-l-propanol. These studies suggested that hot homolytic substitution (SHH2) reactions at sp 3 -hybridized carbon in the gas phase involving monovalent recoil atoms can occur by either of two reaction channels, one with retention of configuration and the other with inversion of configuration.…”