What are the examples of metamerism in organic chemistry give the structure and Iupac name and what is a substitution reaction

Dear student,
Compounds having the same molecular formula but different
number of carbon atoms ( alkyl groups) on either side of functional
group ( i.e., -O-,-S-, -NH-, -C(=O)-) are called metamers and the
phenomenon is called metamerism. Metamerism occurs amongst the members
of the same homologus family. For example,

CH3CH2-O-CH2CH3 is metamer of CH3-O-CH2CH2CH3 OR CH3-O-CH(CH3)2

CH3CH2COCH2CH3 is metamer of CH3COCH2CH2CH3 OR CH3COCH(CH3)2

It may be noted that metamers may also be position isomers, e.g.,
pentan-2-one and pnetan-3-one may be regarded as position isomers as
well as metamers.

for substiution reactions kindly see the link
https://www.askiitians.com/iit-jee-chemistry/organic-chemistry/alkyl-and-aryl-halides/sn1-and-sn2-mechanism.html

For IUPAC nomenclature please see the following link
https://www.askiitians.com/iit-jee-chemistry/organic-chemistry/iupac-and-goc/nomenclature-of-organic-compounds.aspx