Propane protonation state

Enby 6 is an example of a stereospecific elimination reaction of an alkyl halide in which the transition state requires die proton and bromide ion that are lost to be in an anti orientation with respect to each odier. The diastereomeric threo- and e/ytAra-l-bromo-1,2-diphenyl-propanes undergo )3-elimination to produce stereoisomeric products. Enby 7 is an example of a pyrolytic elimination requiring a syn orientation of die proton that is removed and the nitrogen atom of the amine oxide group. The elimination proceeds through a cyclic transition state in which the proton is transferred to die oxygen of die amine oxide group. 

Figure 27. H-carbonium ion-like transition states for methane, ethane, propane and isobutane protonation by HF/SbFs.

Sulfamethoxazole failed to produce any trappable radicals with an array of different spin traps, but naproxen afforded the EPR spectrum shown in Figure 2.11 when irradiated with 330 nm UV-R in the instrument cavity in the presence of 2-methyl-2-nitroso-propane (MNP). The spectrum contains contributions from di-t-butyl nitroxide, a known photoproduct of MNP. The H-atom adduct MNP-H also evident can arise by several different mechanisms, including the trapping of an H atom by MNP the reaction of MNP with an electron followed by protonation and the direct reduction of MNP by an excited state species. In view of the flash photolysis results, it was concluded that photoionization was the major precursor of MNP-H. The third radical corresponded to a C-centered radical carrying a single H atom, leading to the postulate of a decarboxylation reaction as the primary photochemical step. Confirmation of the participation of free radical intermediates came from the initiation of the free radical polymerization of acrylamide with rates as shown in Table 2.1. 

The low yield of 11 is probably a consequence of the endo orientation of the dimethyleyelo-propane ring in transition state E. Formation of cyclodecadiene 13 occurs by rotation of transition state F to give transition state G followed by protonation. Cyclodecadiene 13 is also obtained in the rearrangement of diastereomer 8 via transition state I. 

Figure 14 Mechanisms for the migration of C1 (OH) of propane-1,2-dioi in DDH. Stepwise and concerted mechanisms both require acid cataiysis for the migration of OH from C2 to Cl of propane-1,2-dioi. in the stepwise mechanism, the eiimination of OH from C1 is cataiyzed by proton transfer to form a discrete water moiecuie and oxycation radicai intermediate. Addition of the water moiecuie to Cl with proton transfer compietes the rearrangement, in the concerted mechanism, water is not a discrete intermediate but the migrating oxygen remains partiaiiy bonded to C1 and C2 as weii as hydrogen bonded in a transition state. His143, Asp155, and potassium ion are in contact with the migrating OH group.

A principal product formed by irradiating quinoline-2-carbonitrile (35) in acidified aqueous propan-2-ol has two quinoline rings linked through the 2-4 positions and has lost both cyano-groups. The mechanism put forward for this formal 1,2-addition reaction begins with electron transfer from propan-2-ol to an upper triplet state of protonated (35), followed by attack on a second (ground-state) molecule of (35). A photophysical study of the photoreduction of acridine... 

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