Fluoroalkanes are difficult to prepare directly because flourination of hydrocarbons with pure F₂ gas occurs explosively. Therefore these are prepared by treating alkylchloride or bromide with salts such as Hg₂F₂, AgF.

The reaction is called swarts reaction.

CH₃Br +AgF → CH₃F + AgBr

Aryl halides are less reactive towards nucleophilic substitution because of the partial double bond character of carbon-halogen bonds. It is also partly due to repulsion between the electron cloud of the benzene ring and then ucleophile.

Cl may attack on either side and give a racemic mixture of 2-chloro butane which contain 50% d form and 50%l-form

This reaction occurs in two steps. In first step, acarbocation is formed from alkyl halide molecule.First step is slow step so it is also rate determining step. In second step, an attacking nucleophile attacks on this carbocation and forms the final product.Thus the stability of the carbocationin fluences the rate of reaction. More stable the carbocation, higher is its rate of formation. Thus those alkyl halides which form stable,3º carbocations undergo S_N1 reaction readily. Thus, t-butyl bromide is the favourable substrate

Cl in 2, 4, 6-trinitrochlorobenzene is activated by three NO₂ groups at o, and p-positions and hence undergoes hydrolysis most readily.

Iodoform test is given by methyl ketones, acetaldehyde and methyl secondary alcohols.

Isobutyl alcohol is a primary alcohol hence does'nt give positive iodoform test.

In S_N2 mechanism transition state is pentavalent. Thusbulky alkyl group will be sterically hindered andsmalleralkyl group will favour the S_N2 mechanism. So thedecreasing order of reactivity of alkyl halides is

RCH₂X > R₂CHX > R₃CX