Alkane Structures

Boiling Point When describing the effect of alkane structure on boiling point m Sec tion 2 17 we pointed out that van der Waals attractive forces between neutral molecules are of three types The first two involve induced dipoles and are often referred to as dis persion forces or London forces... 

Thomson Click Organic Interactive to use an online palette to draw alkane structures based on IUPAC nomenclature. 

The same principles just developed for butane apply to pentane, hexane, and all higher alkanes. The most favorable conformation for any alkane has the carbon-carbon bonds in staggered arrangements, with large substituents arranged anti to one another. A generalized alkane structure is shown in Figure 3.10. 

Table 6.4 summarizes the rate constants for the reactions of chlorine atoms with alkanes. Structure-reactivity relationships have again been developed for... 

Alkanes structure, constitutional isomerism, and nomenclature cycloalkanes 11.1-11.5... 

The structures deduced from the mass spectra must account for the observed equivalent chain length (ECL) or Kovats indices (KI) (Carlson et al., 1998 Katritzky and Chen, 2000 Zarei and Atabati, 2005). The values for monomethylalkanes (Mold et al., 1966 Szafranek et al., 1982) can be used to estimate the expected ECL or KI for a di-, tri- or tetramethyl-alkane structure proposed from a mass spectrum. For example, a dimethylalkane, such as 3,11 -dimethylnonacosane, with 31 carbons, would have its elution time decreased by about 0.3 carbons for the 3-methyl group and about 0.7 carbons for the 11-methyl group. Thus, the predicted ECL is approximately 30 and this is the ECL observed. 

You ve seen that a functional group is essentially any deviation from an alkane structure, either because the molecule has fewer hydrogen atoms than an alkane (alkenes, alkynes) or because it contains a collection of atoms that are not C and not H. There is a useful term for these different atoms heteroatoms. A hateroatom is any atom in an organic molecule other than C or H. 

Draw the five alkane structural isomers for the molecular formula CeHu. 

These examples suggest four alkane structures that may be able to undergo non-branching modes of alkyldihydroperoxy radical decomposition, as follows ... 

C. Morley, A Fundamentally Based Correlation between Alkane Structure and Octane Number, Comb. Sci. Tech. 55 (1987) 115. 

No element forms such a variety of hydrides as carbon. In addition to the numerous known alkanes, structural isomerism predicts many... 

The physical properties of the alkanes follow the pattern laid down by methane, and are consistent with the alkane structure. An alkane molecule is held together entirely by covalent bonds. These bonds either join two atoms of the same kind and hence are non-polar, or join two atoms that differ very little in electronegativity and hence are only slightly polar. Furthermore, these bonds are directed in a very symmetrical way, so that the slight bond polarities tend to cancel out. As a result an alkane molecule is either non-polar or very weakly polar. 

Most alkenes contain not only the carbon-carbon double bond but also alkyl groups, which have essentially the alkane structure. Besides the addition reactions characteristic of the carbon-carbon double bond, therefore, alkenes may undergo the free-radical substitution characteristic of alkanes. The most important of these addition and substitution reactions are summarized below, and will be discussed in detail in following sections. 

Since these alkyl groups have the alkane structure, they should undergo alkane [Reactions, for example, substitution by halogen. But an alkene molecule presents two sites where halogen can attack, the double bond and the alkyl groups. Can we direct the attack to just one of these sites The answer is yes, by our choice of experimental conditions. 

By now you have noticed that names of alkanes end in -ane. Also, alkanes with five or more carbons in a chain have names that use a prefix derived from the Greek or Latin word for the number of carbons in each chain. For example, pentane, has five carbons just as a pentagon has five sides, and octane has eight carbons just as an octopus has eight tentacles. Because methane, ethane, propane, and butane were named before alkane structures were known, their names do not have numerical prefixes. Table 22-1 shows the names and structures of the first ten alkanes. Notice the underlined prefix representing the number of carbon atoms in the molecule. 

Organic molecules containing functional groups are given lUPAC names based on their main-chain alkane structures. For the alkyl halides, a prefix indicates which halogen is present. The prefixes are formed by changing the -ine at the end of each halogen name to -o. Thus, the prefix for fluorine is fluoro-, chlorine is chloro-, bromine is bromo-, and iodine is iodo-. 

Medium and large rings can be formed in thermal, photochemical, and other reactions of compounds containing the bicyclo[n.l. 0]alkane structural unit with n > 5. They are also formed in a variety of unique rearrangements, and in ring-expansion reactions proceeding via bi-cyclo[n. 1. OJalkan-1 -oxyl radicals. 

If equimolar quantities of tetramethylammonium fluoride and a threefold excess of Me3SiCF3 or its homologues are used the perfluoroalkyltrimethyl silane acts as an effective source of nucleophilic perfluoroalkyl equivalents for nucleophilic substitution of aliphatic triflates [90] (Scheme 2.136). This method enables the simple synthesis of partially fluorinated alkane structures which are of interest in the chemistry of liquid crystals and other functional materials. 

When writing out alkane structures, you can use different levels of shorthand depending on the needs at hand. For example, pentane can be written out... 

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