Theory of Organic Chemistry and Isomerism

Butlerov's Theory

Main principles of A. M. Butlerov (1861):

• Atoms are bonded in a definite order according to their valences.
• Properties depend on chemical structure, not only on composition.
• Atoms influence each other.

Isomers and Homologs

• Isomers: substances with the same composition but different structure. Their properties are also different.
• Homologs: differ by CH₂ (14 mass units). Their structure is similar.

Types of Isomerism

Isomerism	Example
Skeletal (chain)	butane / isobutane
Positional	1-butene / 2-butene
Interclass	alcohol / ether
Geometric	cis- / trans-

There is also optical isomerism.

• Positional: the position of a double bond or functional group.
• Interclass: C₂H₅OH and CH₃OCH₃.
• Geometric: due to the lack of free rotation around the double bond. 2-butene: cis and trans.
• Optical: asymmetric C: 4 different substituents.

Interclass Isomers

• Alkene ↔ cycloalkane: CₙH₂ₙ.
• Alkyne ↔ alkadiene: CₙH₂ₙ₋₂.
• Alcohol ↔ simple ether: CₙH₂ₙ₊₂O.
• Aldehyde ↔ ketone: CₙH₂ₙO.
• Acid ↔ ester: CₙH₂ₙO₂.

Number of Alkane Isomers

C₄H₁₀: 2, C₅H₁₂: 3, C₆H₁₄: 5, C₇H₁₆: 9