Sec-butyl groups

The C4H9 alkyl groups may be derived either from the unbranched carbon skele ton of butane or from the branched carbon skeleton of isobutane Those derived from butane are the butyl (n butyl) group and the 1 methylpropyl (sec butyl) group... 

Schiffbase, 1147 Scurvy vitamin C and, 772 sec-Butyl group, 84 Second-order reaction, 363 Secondary alcohol, 600 Secondary amine, 917 Secondary carbon, 84 Secondary hydrogen. 85 Secondary structure (protein), 1038-1039... 

Chemical structure. The structure of the free base of Cypridina luciferin (C22H27ON7, Mr 405.50) was determined by Kishi et al. (1966a,b) as shown below (A) its sec-butyl group is in the same configuration as in L-isoleucine. The structure of oxyluciferin reported by the same authors contained an error, and the structure was corrected later as shown in Fig. 3.1.8 (McCapra and Chang, 1967 Stone, 1968). 

The yield of 17 is 50 62% in the reactions involving butyl- or. vw-butyllithium due to competitive transfer of the butyl or sec-butyl group. Yields of 17 are improved by using pyridine as the additive, but diastereoselectivity is not as high as when the alkyllithiums are employed. Without any additive, a complex mixture of syn- and anti-diastereomers plus products resulting from addition of the a-carbon of the substrate borane to the aldehyde are obtained. 

The reaction of bromine with optically active sec-butyltin compounds Bu SnRs, to give sec-butyl bromide, can give retention or inversion in the sec-butyl group, depending on the natime of the group R... 

B Pentane is a five-carbon chain. There is a — CH3 group on carbon 2, a sec-butyl group on carbon 3. 

All the crystal forces that we treat in this section can be considered in terms of the recognition between a given, reference molecule and the cavity it is to occupy in the crystal. In chiral systems the cavity is clearly of different shape in the d and / crystals, and this generally results in differential incorporation of R and S molecules. However, in molecules containing the sec-butyl group, discrimination is often ineffective. This is because the two enantiomers can assume different conformations with very similar external shapes, and they can then interchangeably enter the same cavity in the crystal. This effect was recognized some time ago (55), and recently its consequences have been studied in detail (56). In the case where two enantiomers may readily replace one another in the crystal, it follows that there is a tendency to conformational disorder (see biphenyl, above), and in many cases, the resolved enantiomers and the racemates are isostructural. 

Two types of geometric effects have been found in this context. One of these effects is exemplified by isoleucine (16), in which the sec-butyl group adopts a gauche conformation and disorder occurs through interchange of ethyl and methyl groups (57). In this situation the sec-butyl group has pseudo mirror symmetry. 

Similarly, there are four different kinds of butyl groups. Two (butyl and sec-butyl) are derived from straight-chain butane, and two (isobutyl and tert-butyl) are derived from branched-chain isobutane. The prefixes sec- (for secondary) and tert- (for tertiary) refer to the number of other carbon atoms attached to the branching carbon. There are two other carbons attached to the branch point in a sec-butyl group and three other carbons attached to the branch point in a tert-butyl group. 

Figure 1 Structure of the avermectin molecule. As discussed in the text, there are eight naturally occurring, structurally related avermectins, which arise from the presence of (1) either a methoxy or a hydroxyl group at C5 (OR3), (2) the presence of either double-bond carbons at C22,23 or a hydroxyl group at C23 (Ri), and (3) the presence of either a methyl or an ethyl residue (R2) located at the isopropyl or the sec-butyl group, respectively, that is attached to C25.

Replacement of the isopropyl groups of la by sec-butyl groups has little effect on... 

Isoleucine has a sec-butyl group for its side chain. Remember that CH3 — CHO undergoes Strecker synthesis to give alanine, with CH3 as the side chain. Therefore, sec-butyl—CHO should give isoleucine. 

There are two more isomers of the butyl group, both of which have common names and abbreviations. The sec-butyl group (s-butyl or s-Bu) has a methyl and an ethyl group joined to the same carbon atom. It appears in an organolithium compound, sec-butyl lithium, used to introduce lithium atoms into organic molecules. 

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