Ab initio characterization of ring-opening H-transfer in ionized cyclopentanone: Similarity to ion-neutral
1Marine Biomedical Institute, University of Texas Medical Branch, 301 University Boulevard, 77555-1069, Galveston, TX.
Abstract:
Ab initio procedures were used to characterize the transition states for α-cleavage and subsequent H-transfer starting with ionized cyclopentanone (1). The objective was to determine whether the parts of the ion disconnected by the bond cleavage remain in close association through the H-transfer. The transition state for C-C bond cleavage is close in energy to the resulting distonic ion, which is a stable species, and far in geometry from any transition state involving H-transfer. We find no evidence for any concertedness or "quasiconcertedness" in this reaction. Ring-opening H-transfer in 1 and ion-neutral complex-mediated alkane eliminations are compared.
Related Concept Videos
02:38Electrophilic Addition to Alkynes: Halogenation
Halogenation is another class of electrophilic addition reactions where a halogen molecule gets added across a π bond. In alkynes, the presence of two π bonds allows for the addition of two equivalents of halogens (bromine or chlorine). The addition of the first halogen molecule forms a trans-dihaloalkene as the major product and the cis isomer as the minor product. Subsequent addition of the second equivalent yields the tetrahalide.
01:18Aromatic Hydrocarbon Cations: Structural Overview
Removing one hydrogen from the intervening CH2 group...
01:17Thermal Electrocyclic Reactions: Stereochemistry
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
02:25Elimination Reactions
01:11Nucleophilic Aromatic Substitution: Elimination–Addition
01:21Acid-Catalyzed α-Halogenation of Aldehydes and Ketones
In the first step of the mechanism, the acid protonates the carbonyl oxygen resulting in a resonance-stabilized cation, which subsequently loses an α-hydrogen to form an enol tautomer. The C=C bond in an enol is highly nucleophilic because of the electron-donating nature of the –OH group. Consequently, the double bond attacks an electrophilic...