Chemistry · Ch 14 — Haloalkanes and Haloarenes
Physical Properties
Physical Properties
(1) Pure haloalkanes are colourless; bromo- and iodo-alkanes develop colour on standing in light. (2) Haloalkanes with one to three carbons are gases at room temperature; beyond three carbons they are liquids or solids. (3) Boiling and melting points: (i) haloalkanes boil and melt higher than the parent alkane of the same carbon count, because dipole-dipole interaction adds to the van der Waals forces already present; (ii) for a given alkyl group, boiling/melting point falls with the halogen in the order CH3I > CH3Br > CH3Cl > CH3F; (iii) for a given alkyl group, boiling point rises with the number of halogen atoms, e.g. CCl4 > CHCl3 > CH2Cl2 > CH3Cl; (iv) for a fixed halogen, boiling/melting point rises with the number of carbons, e.g. CH3CH2CH2Cl > CH3CH2Cl > CH3Cl; (v) among isomeric alkyl halides, boiling point falls as branching increases, because a more branched, more spherical molecule has less surface area for intermolecular contact, e.g. 1-chlorobutane (351.5 K) > 2-chlorobutane (341 K) > 2-chloro-2-methylpropane (324 K). (4) Solubility: haloalkanes are polar covalent compounds, solu …
Worked out. Book's practice box (no printed solution): write all possible chain isomers of C5H11Cl. There are eight monochloro isomers of pentane: 1-chloropentane (n-pentyl chloride), 2-chloropentane, 3-chloropentane, 1-chloro-2-methylbutane, 2-chloro-2-methylbutane (tert-amyl chloride), 2-chloro-3-methylbutane, 1-chloro-3-methylbutane (isoamyl chloride) and 1-chloro-2,2-dimethylpropane (neopentyl chloride) -- one for each chemically distinct hydrogen across pentane's three carbon skeletons (n-pentane, 2-methylbutane and 2,2-dimethylpropane) (own solution, n …