Stereochemistry of Hot Hydrogen Displacement at sp³ Carbon-Hydrogen Bonds

Chemical Kinetics and Hot Atom Chemistry — Present Status and Future Perspectives

“…Greater than 80 % inversion has been observed when high energy 38 CI and 34m Cl atoms replace a covalently bonded chlorine at the chiral center of 2-chloropropionyl chloride at gas-phase pressures of 0.5-0.8 atm [9], Here the asterisk indicates that the recoiling 38 CI atoms are translationally excited. These findings contrast with previous stereochemical studies in which observations of retention of configuration accompanying recoil tritiumfor-hydrogen (T-for-H) atomic substitution [10][11][12][13][14][15]have been interpreted within the context of a 3-center direct, or "impact" [3,4], reaction model. 2 Although evidence has also been available for many years supporting the occurrence of inverting hot T-for-H and Cl-for-Cl reaction modes [16][17][18][19][20][21][22][23][24][25][26][27], the significance of the available gas phase results has often been challenged.…”

The stereochemistry of energetic chlorine atom exchange in alkyl halides

“…22 Analogous observations of retention of configuration during T-for-H substitution have been reported for several experiments with energetic tritium atoms from nuclear recoil. [23][24][25][26] The almost complete absence of the inversion product in gas-phase experiments with energetic chlorine atoms implies either that the motions of the substituent groups required for the inversion process take too much time for completion while the hot Cl atom is available for bonding, or else these rapid motions involve so much vibrational excitation energy that the molecules thus formed undergo secondary decomposition within 10-10 sec, and hence are not experimentally observed in the gas phase.…”

Recoil Reactions of Tritium with Organic Compounds

“…in crystalline L-(+)-alanine, occurred with almost complete retention of the configuration. Later, Wolfgang et al [19] found over 90% retention of configuration in gas-phase experiments with secondary butyl alcohol, and showed further that about 70 % of cis-and trans-dichloroethylene remained in the original conformation after the tritium hydrogen exchange [20]. These results imply a very rapid, direct exchange mechanism.…”