For additions of hydrogen

Enthalpy for addition of hydrogen to give the corresponding bicycloalkane... 

The order of reactivity of the hydrogen halides is HI > HBr > HCl, and reactions of simple alkenes with HCl are quite slow. The studies that have been applied to determining mechanistic details of hydrogen halide addition to alkenes have focused on the kinetics and stereochemistry of the reaction and on the effect of added nucleophiles. The kinetic studies often reveal complex rate expressions which demonstrate that more than one process contributes to the overall reaction rate. For addition of hydrogen bromide or Itydrogen... 

The anti-Markownikoff addition of hydrogen bromide to alkenes was one of the earliest free-radical reactions to be put on a firm mechanistic basis. In the presence of a suitable initiator, such as a peroxide, a radical-chain mechanism becomes competitive with the ionic mechanism for addition of hydrogen bromide ... 

Product mixtures from radical-chain addition of hydrogen chloride to alkenes are much more complicated than is the case for addition of hydrogen bromide. The problem is that the rate of abstraction of hydrogen from hydrogen chloride is not fast relative to the rate of addition of the alkyl radical to the alkene. This results in the formation of low-... 

The greater stability of the digonal vinyl cation 161 than of the bridged cation 162 would imply that, at least in the gas phase, race-mization is involved as stereochemical course of any reaction with nucleophiles since both lobes of the empty p-orbital of 161 are available for a nucleophilic attack. Efforts to rationalize (Bumelle, 1964) early reports of stereospecific trans addition to acetylene derivatives have recently been complemented by a theoretical calculation of the energy profile for addition of hydrogen fluoride to acetylene in the gas phase (Hopkinson et at., 1971). The results of these calculations suggest that the bridged cation is possibly a transition state and not an intermediate. 

When the solution is saturated, copious fumes of hydrogen chloride are evolved from the vent. The reaction should not be continued beyond this point. With an ice-salt bath the time required for addition of hydrogen chloride was 35 minutes. 

The commonly accepted mechanism for addition of halogens to alkenes has two steps, and is quite analogous to the mechanism for addition of hydrogen-containing acids (protic acids). In step (1) halogen adds as a positive halogen ion... 

For addition of hydrogen cyanide to cyclopropanone see Section 5.2.3.5.6.1. The reaction of 2-(trimethylsilyl)cyclopropanone (6) with neat trifluoroacetic anhydride at room temperature afforded l,l-bis(trifluoroacetoxy)cyclopropane (7) in quantitative yield. ... 

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