Organic Chemistry Key Concepts: Alkanes & Cycloalkanes
-Straight or branched chain compounds of carbon and hydrogen are termed acyclic hydrocarbons or
alkanes. Alkanes are unreactive as the electrons are perfectly balanced between the atoms and the
carbon-carbon bonds are quite durable. All alkanes fit the general formula: C n 2n + 2
-Constitutional isomers are compounds that have the same molecular formula but different bonding
sequences (properties). When drawing possible constitutional isomers, remember to concentrate on the
C atom bonding sequence.
-The “dot-line-wedge” is the most versatile, widely-used convention for the 3-dimensional drawing of
molecules. Atoms in molecules always spin around σ bonds. Newman projections and Fischer
projections are also used extensively.
-Differing short-lived spatial arrangements of atoms, termed conformations, can result from the rapid
rotation of atoms, or groups of atoms, about single bonds. Staggered conformations are of slightly lower
energy than eclipsed ones. Conformations cannot normally be separated or isolated and are therefore
-Hydrocarbons closed to form a ring are known as cycloalkanes. Cycloalkanes fit the general formula
CnH 2ncause two Hs have to be removed from an alkane to allow the ring to form.
-The boat conformation of cyclohexane is present in the conformation equilibrium mixture in very small
amounts. The chair