# 14.2: Physical Properties of Organohalogen & Organometallic Compounds

The physical properties of haloalkanes are much as one might expect. Volatility decreases: (a) with increasing molecular weight along a homologous series, (b) with increasing atomic number of the halogen, and (c) with the structure of the alkyl group in the order such that tertiary $$<$$ secondary $$<$$ primary for isomeric halides. These trends are apparent from the physical properties listed in Table 14-1, which includes data for simple halogen derivatives of alkanes, alkenes, alkynes, and arenes.

Table 14-1: Physical Properties of Organic Halides

The boiling points of many halogen compounds are similar to hydrocarbons of the same molecular weight, but there are some conspicuous exceptions. lodomethane, for example, has about the same molecular weight as decane (MW 142), but the boiling point of iodomethane is $$132^\text{o}$$ lower than that of decane. Likewise, fluorocarbons (e.g., tetrafluoromethane, $$\ce{CF_4}$$, MW 88, bp $$-129^\text{o}$$) are far more volatile than hydrocarbons of similar weights (e.g., hexane, $$\ce{C_6H_{14}}$$, MW 86, bp $$69^\text{o}$$).

In general, halogen compounds are insoluble in water but are readily soluble in organic solvents and, with the exception of some fluoro and monochloro compounds, they are more dense than water. Aryl halides are fairly pleasant smelling liquids, but arylmethyl (benzylic) halides of structure $$\ce{ARCH_2X}$$ are irritating to the eyes, skin, and nasal passages. Toxicity varies, but the chlorinated hydrocarbons such as $$\ce{CCl_4}$$ (“carbon tet”) and $$\ce{CHCl_2-CHCl_2}$$ are quite toxic and should be used with care.

## Contributors

• John D. Robert and Marjorie C. Caserio (1977) Basic Principles of Organic Chemistry, second edition. W. A. Benjamin, Inc. , Menlo Park, CA. ISBN 0-8053-8329-8. This content is copyrighted under the following conditions, "You are granted permission for individual, educational, research and non-commercial reproduction, distribution, display and performance of this work in any format."