In cyclic systems, this type of reaction interconverts cis and trans stereochemical relations.  
In cyclic systems, this type of reaction interconverts cis and trans stereochemical relations.  Branching at or near the reacting carbon slows it down, because of steric hindrance and the energy required to attain a gauche methyl-halide conformation.  It is impeded by solvation and proceeds by the backside attack of an electrophilic carbon, with the nucleophile replacing the weak base for a leaving group.  FTP name this stereospecific, concerted, one-step displacement reaction mechanism following a second-order rate law.
In cyclic systems, this type of reaction interconverts cis and trans stereochemical relations.  
SN2 or substitution nucleophilic second order or bimolecular nucleophilic substitution