Alkyl groups simple

Bromoadamantane couples with CH3MgBr in ethyl ether solution at 100 °C to give 1-methyladamantane in 83 % yield 201 While similar coupling reactions are not synthetically useful or do not occur at all with other alkyl groups, simple alternative synthetic methods have been developed. 

Depending on the nature of the alkyl group, simple diaUcylzinc compounds can be mobile liquids or low-melting solids (Table 1). They are all colorless and completely miscible with common nonprotic solvents. With polar see Polar... 

Some of the common aromatics found in crude oil are the simple derivatives of benzene in which one or more alkyl groups (CHg) are attached to the basic benzene molecule as a side chain which takes the place of a hydrogen atom. These arenes are either liquids or solids under standard conditions. 

The effect of alkyl groups in the 5-position on the reactivity of the thiazole nitrogen is analogous to that found for 3-alkylpyridines, in other words, a simple inductive effect. In passing from the unsubstituted heterocycle to the methyl derivative, the rate constant doubles a further increase in substitution produces a much less pronounced variation. 

In practice this reaction is difficult to carry out with simple aldehydes and ketones because aldol condensation competes with alkylation Furthermore it is not always possi ble to limit the reaction to the introduction of a single alkyl group The most successful alkylation procedures use p diketones as starting materials Because they are relatively acidic p diketones can be converted quantitatively to their enolate ions by weak bases and do not self condense Ideally the alkyl halide should be a methyl or primary alkyl halide... 

Protonolysis. Simple trialkylboranes are resistant to protonolysis by alcohols, water, aqueous bases, and mineral acids. In contrast, carboxyUc acids react readily with trialkylboranes, removing the first alkyl group at room temperature and the third one at elevated temperatures. Acetic and propionic acids are most often used. The reaction proceeds with retention of configuration of the alkyl group via a cycHc, six-membered transition state (206). 

The nitrosation of pyrroles and indoles is not a simple process. The 3-nitroso derivatives (84) obtained from indoles exist largely in oximino forms (85) (80IJC(B)767). Nitrosation of pyrrole or alkylpyrroles may result in ring opening or oxidation of the ring and removal of the alkyl groups. This is illustrated by the formation of the maleimide (86) from 2,3,4 -trime thylpyrrole. 

Experimental pKa data suggests that simple alkyl groups all affeet acid-base reactivity in roughly the same way. What is more, this universal alkyl effect is roughly equivalent to the effect of a hydrogen atom. For example, the difference in pKa between water and ethanol is approximately the same as that between formic acid and propanoic acid (see table at right). 

Amination of the deactivated carbanion of 4-benzylpyridine formed with excess sodamide presumably proceeds because the strong indirect deactivation is overcome by electrophilic attack by Na+ at the partially anionic azine-nitrogen and by concerted nucleophilic attack by H2N at the 2-position via a 6-membered cyclic transition state (75). However, in simple nucleophilic displacement a carbanion will be more deactivating than the corresponding alkyl group, as is true in general for anionic substituents and their non-ionic counterparts. 

Another point for structural diversification is the sulfonamide group. Imai had already shown that a wide variety of groups could be introduced at this position to optimize the reaction. Since a wide variety of sulfonyl chlorides are commercially available, a number of different types of groups could be examined (Scheme 3.34). Testing of a variety of aryl and alkyl groups on the 1,2-cyclohexanediamine backbone demonstrates that the simple methanesulfonamide 122 is clearly superior or equal to many other analogs in the cyclopropanation of cinnamyl alcohol (Table 3.11). Another concern which was directly addressed by this survey was the question of catalyst solubility. 

The transfer of simple alkyl groups (R in the table—mostly -Bu or Me), from tin to palladium complex 6 is a very slow process, and the substituent R (see table) is transferred selectively. The leaving group X on the coupling component... 

Recently, an interesting reaction of -dinitrobenzene v/ith trialkylborane has been reported, in which the iritro group is replaced by an alkyl group in good yield fEq 913 " The reacdon is not a simple ionic reacdon, but proceeds via free radical intermediates... 

The common names of these simple alkyl groups are so well entrenched in the chemical literature that IUPAC rules make allowance for them. Thus, the following compound is properly named either 4-(l-methvlethyl)heptane or 4-iso-propylheptane. There is no choice but to memorize these common names fortunately, there are only a few of them. 

In addition to their systematic names, many simple alkyl halides are also named by identifying first the alkyl group and then the halogen, for example, CH3T can be called either iodomethane or methyl iodide. Such names are well entrenched in the chemical literature and in daily usage, but they won t be used in this book. 

The equilibrium situation for simple substituted 2-ulkenyl alkali metal derivatives can be estimated by a rule of thumb electron-accepting and electropositive substituents ( ) prefer the exo position, but electron-donating and electronegative substituents ( ), including alkyl groups, tend to occupy the endo position. With increasing steric demand of the substituent, the exoisomer becomes more favored. 

Alkyl substituents that bear a functional group may be converted into simple unsubstituted alkyl groups in several ways, as illustrated briefly in the following examples. The reverse processes are covered in Section 2.2.4. 

The concept of hyperconjugation arose from the discovery of apparently anomalous electron-release patterns for alkyl groups. By the field effect alone, the order of electron release for simple alkyl groups connected to an unsaturated system is fert-butyl > isopropyl > ethyl > methyl, and this order is observed in many phenomena. Thus, the dipole moments in the gas phase of PhCHa, PhC2Hs, PhCH(CHa)2, and PhC(CHa)a are, respectively, 0.37, 0.58, 0.65 and 0.700. ... 

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