Carboxylic acid derivatives react with nucleophiles in nucleophilic acyl substitution. An alternative to aromatic substitution is electrophilic aliphatic substitution. Toluene reacts as a normal aromatic hydrocarbon in electrophilic aromatic substitution. S2 is a kind of nucleophilic substitution reaction mechanism. Like phenols, aniline derivatives are highly susceptible to electrophilic substitution reactions. There is a certain level of competition between the elimination reaction and nucleophilic substitution. It is an example of a radical-nucleophilic aromatic substitution. The Sandmeyer reaction is an example of a radical-nucleophilic aromatic substitution (SAr). Another way is to do an oxidation before the electrophilic substitution. The Feistel cipher uses a combination of substitution and transposition techniques. The majority of these consist of point mutations causing substitution of amino acids. Silent mutations code for the same amino acid (a "synonymous substitution"). E1cb elimination always compete with the S1 substitution. The mass can be eliminated by the (trivial) substitution formula 82. An increasing substitution of R increases affinity.