Constitutional Isomer
Constitutional isomers (also called structural isomers) are molecules that share the same molecular formula but differ in the connectivity of their atoms — that is, in which atoms are bonded to which. They are distinct compounds with different physical and chemical properties, such as boiling point, melting point, and reactivity. Constitutional isomerism is the most basic form of isomerism and is distinct from stereoisomerism, where connectivity is the same but spatial arrangement differs.
Constitutional Isomers of Molecular Formula C4H10
| Isomer Name | Structural Formula | Boiling Point (°C) | Carbon Skeleton | IUPAC Name |
|---|---|---|---|---|
| n-Butane | CH3-CH2-CH2-CH3 | -1 | Straight chain (4C) | Butane |
| Isobutane | (CH3)3CH | -12 | Branched (1° branch) | 2-Methylpropane |
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Related Terms
IUPAC Nomenclature
IUPAC nomenclature is the systematic method for naming chemical compounds, developed and maintained by the International Union of Pure and Applied Chemistry (IUPAC). For organic compounds, it provides an unambiguous, internationally recognised name based on the longest carbon chain (parent chain), substituents, and functional groups, enabling chemists worldwide to communicate compound structures without ambiguity. The rules cover alkanes, alkenes, alkynes, halides, alcohols, carboxylic acids, and all other organic functional groups.
Markovnikov's Rule
Markovnikov's Rule states that when a protic acid (HX) adds to an unsymmetrical alkene, the hydrogen atom bonds to the carbon that already bears the greater number of hydrogen atoms, while the halide or nucleophile bonds to the more substituted carbon. This regioselectivity arises because the reaction proceeds through the more stable (more substituted) carbocation intermediate. The rule is foundational for predicting the major product of electrophilic addition reactions in organic synthesis.
Free Radical
A free radical is a highly reactive chemical species containing one or more unpaired electrons in its outermost orbital. Free radicals are typically short-lived and can be derived from atoms, molecules, or ions by homolytic cleavage of a covalent bond. They play key roles in combustion, atmospheric chemistry, polymerisation, and biological oxidative stress, where they can damage DNA, proteins, and lipids.
From Latin 'constitutio' (arrangement, composition) and Greek 'isos' (equal) + 'meros' (part). The term 'isomer' was introduced by Jöns Jacob Berzelius in 1830; 'constitutional isomer' became the IUPAC-preferred term in the 20th century to distinguish connectivity-based isomerism from stereoisomerism.