Restricted rotation around C=N (oximes) gives rise· to geometrical isomerism in oximes. Here 'syn' and 'anti' are used instead of cis and trans respectively. In the syn isomer the H atom of a doubly bonded carbon and -OH group of doubly bonded nitrogen lie on the same side of the double bond, while in the anti isomer, they lie on the opposite side of the double bond. For Eg:

Homologous series: A series of organic compounds each containing a characteristic functional group and the successive members differ from each other in molecular formula by a CH₂ group is called homologous series.
Alkanes: Methane (CH₄), Ethane (C₂H₆), Propane (C₃H₈) etc.
Alcohols: Methanol (CH₃OH), Ethanol (C₂H₅OH) Propanol (C₃H₇OH) etc. Compounds of the homologous series are represented by a general formula.
Alkanes C_nH_2n+2, Alkenes C_nH_2n, Alkynes C_nH_2n-2 and can be prepared by general methods. They show regular gradation in physical properties but have almost similar chemical property.

The term 'isomerism' was given by Berzelius, and its represents of existence of two or more compounds with the same molecular formula but different structure and properties (physical, chemical, or both). Compounds exhibiting this isomerism are called isomers. The difference in properties of two is omers is due to difference in (bond connectivity or spatial arrangement) the arrangement of atoms within their molecules. Isomerism is broadly divided into two types
i. Constitutional isomerism
ii. stereoisomerism.

Molecular stucture can be derived from the type of hybridisation. An Sp₃ hybridised carbon will have a tetrahedral geometry, a Sp₂ hybridised carbon will have trigonal planar geometry and sp hybridised carbon will have a linear geometry.