Tertiary hydrogen replacement

In practice this means that when an alkane contains primary secondary and tertiary hydrogens it is usually only the tertiary hydrogen that is replaced by bromine... 

Fluorination of aliphatic hydrocarbons with cobalt trifluoride gives complex mixtures Isobutane (2-methylpropane) fluorinated at 140-200 °C affords a mixture of 30 products of different degrees of fluorination and of isobutane as well as butane skeletons. The tertiary hydrogen is replaced preferentially Products containing 5-10 atoms of fluorine including a small amount of perfluoroisobutane were isolated [10]. 

Due to the highly exothermic nature of the process, the replacement of primary, secondary and tertiary hydrogens upon reaction with electrophilic fluorine atoms is not as selective as for other radicals. For example, early work by Tedder [30,34], showed that the order of selectivity follows the usual pattern, i. e. tert > sec > prim, but the relative selectivity of fluorine atoms is less than chlorine atoms (Table 2). 

Elemental fluorine can be used to replace relatively electron rich C-H bonds by C-F. In particular, tertiary hydrogen atoms which are remote from electron withdrawing substituents can be selectively replaced by fluorine and, where there is more than one tertiary hydrogen atom in the substrate, that with the higher electron density is replaced (Fig. 44). In contrast, where there is an electron withdrawing group close to tertiary hydrogen, very little reaction with fluorine takes place and, consequently, when one fluorine atom has been introduced into a molecule further reaction is often inhibited. 

In some esters, bromine trifluoride selectively replaces the tertiary hydrogen atom with fluorine.127 The reaction is carried out in CFC-113 at 25-35 C with 60-80% excess bromine trifluoridc. The products are obtained in 40-50% yield. 

Hydrogen attached to a tertiary hydrogen is most readily substituted secondary hydrogens are only very slowly replaced, while primary hydrogens are quite unreactive. Alkylaromatics react preferentially at the benzylic position. The reaction is accompanied by oxidation to yield carbonyl compounds, acids, and carbon oxides. Other main byproducts are nitrites, alcohols, and large quantities of poly-nitro compounds. 

SAMPLE SOLUTION (a) Write the structure of the starting hydrocarbon, and identify any tertiary hydrogens that are present. The only tertiary hydrogen in methylcydopentane is the one attached to C-1. This is the one replaced by bromine. 

Palmer and Lossing (73) obtained analogous results with isobutane. Thus for iso-CiHio, the relative primary yields of terl-butyl to isobutyl radicals were found to be in the ratio, 7 1. However, when the tertiary hydrogen atom in the molecule was replaced by deuterium this ratio dropped to about 1 2. 

Definitions of primary, secondary, and tertiary hydrogens. There are six primary hydrogens in propane and only two secondary hydrogens, yet the major product results from replacement of a secondary hydrogen. 

Amines are a series of compounds containing carbon, hydrogen and nitrogen. They are part of the building blocks for the important protein molecules involved in metabolic processes. Amines are compounds similar to ammonia, but have one or more of their hydrogens replaced by a carbon chain, e.g. CH3. When one hydrogen of ammonia is replaced, the series is called the primary amines (Figure 5.1) with two Hs replaced, the series is called the secondary amines, and with all three replaced, tertiary amines. 

Purification of MTBE (b.p. 55°C) for general solvent use is by distillation. Its use in general solvent applications is still small. However, since MTBE has no secondary or tertiary hydrogens it is very resistant to oxidation and peroxide formation. This makes it an attractive replacement for the more traditional diethyl, and diisopropyl ethers. 

Fluorination of active-methylene compounds [1, 803, after citation of ref. 3]. Fluorination of an enolate activated by only one carbonyl group has been observed. Thus the sodioenolate of methyl isobutyrate on treatment with perchloryi fluoride gives 4-fluoro-3-keto-2.2.4-trimethylpentanoate as the only pure product in 30% yield. It is possible that this fluorination is successful only in the case of replacement of a tertiary hydrogen.38... 

This polymer is different from polymethylvinylketone in that the replacement of the tertiary hydrogen atom of each monomeric unit by a methyl group prevents the occurrence of the Norrish type II reaction in so far as a six-membered ring transition state is involved. On exposure to 313 nm radiation at 150—180°C in vacuo, solid polymethylisopropenylketone undergoes depolymerization with a quantum yield of about 5 [Ref. 11]. The mechanism proposed is... 

Each of the two fluorine atoms in the fluorine molecule is a strong electron acceptor. This property is responsible for the partial electrophilic behavior of elemental fluorine under certain circumstances and selective fluorinations of organic compounds with elemental fluorine have been reviewed on several occasions12 84,85. Tertiary hydrogens in steroids are preferably replaced by fluorine with retention of configuration86 87. 

Allylic bromination by NBS can be applied with success not only to olefins but also to <%,/ -unsaturated ketones, carboxylic esters, nitriles, and lactones. Radical-formers must be added when NBS is used for allylic bromination of conjugated dienes, for side-chain bromination of aromatic or heterocyclic compounds (see p. 198), or for replacement of tertiary hydrogen atoms next to a C=C bond. 

The nitrogen of an amine has the same geometry it has in ammonia (Section 1.12). One, two, or three hydrogens may be replaced by alkyl groups. The number of hydrogens replaced by alkyl groups determines whether the amine is primary, secondary, or tertiary (Section 2.7). 

Similarly, bromination of 2,2,5-trimethyUiexane gives an 82% yield of the product in which bromine replaces the tertiary hydrogen. Chlorination of the same alkane results in a 14% yield of the tertiary alkyl chloride (Section 9.3). 

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