Chemistry · General Principles Of Organic Chemistry · NEET
In structural isomerism the atoms are joined in a different order, so the connectivity of bonds itself changes (like chain, position, functional, metamerism). In stereoisomerism the connectivity is exactly the same — same atoms bonded to the same atoms — only the position of groups in 3D space differs. NCERT states stereoisomers have the same constitution and sequence of covalent bonds but differ in the relative positions of their atoms or groups in space.
Geometrical isomerism (also called cis-trans isomerism) and optical isomerism. Geometrical isomerism comes from restricted rotation, usually around a C=C double bond or a ring. Optical isomerism comes from chirality (a molecule that is non-superimposable on its mirror image), usually because of a chiral carbon.
Yes. Cis-trans (geometrical) isomerism is one of the two branches of stereoisomerism. Cis means the two similar groups are on the same side of the double bond; trans means they are on opposite sides. Because you cannot rotate around a C=C bond freely, these two forms cannot convert into each other, so they are separate isomers.
No, be careful here. Conformations arise from free rotation around a C-C single bond and interconvert easily, so they cannot be separated. NCERT notes different conformational isomers of ethane have not been isolated. True stereoisomers (geometrical, optical) cannot freely interconvert, so they are distinct, separable compounds. This is a common NEET trap.
Yes. All isomers, including stereoisomers, share the same molecular formula. Stereoisomers go further: they also have the same bond connectivity. The only difference is the 3D orientation of the groups, which is why you must draw them in space (wedge-dash or across a double bond) to tell them apart.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
It is when two molecules have the same formula and the same bonds joining the same atoms, but the atoms or groups point in different directions in 3D space, making them different compounds.
Geometrical (cis-trans) isomerism and optical isomerism.
It is a fixed part of the isomerism topic. Questions ask you to classify a pair of structures as structural, geometrical, or optical isomers, and to spot conditions like a C=C double bond or a chiral carbon.
Restricted rotation around a carbon-carbon double bond (or a ring), when each doubly bonded carbon carries two different groups.
Chirality — a molecule that is not superimposable on its mirror image, usually because of a chiral carbon bonded to four different groups. This leads to enantiomers.
