6-Methylheptane-2-one

The product is the racemic [(R)/(S)] alcohol since the free energies of the two diastereoisomeric transition states, resulting from hydride attack on the si-face of the ketone as shown (order of priorities O > R1 > R2, p. 16) or the re-face, are identical. The use of an aluminium alkoxide, derived from an optically pure secondary alcohol, to effect a stereoselective reaction (albeit in low ee%) was one of the first instances of an asymmetric reduction.48 Here (S)-( + )-butan-2-ol, in the form of the aluminium alkoxide, with 6-methylheptan-2-one was shown to give rise to two diastereoisomeric transition states [(5), (R,S) and (6), (S,S)] which lead to an excess of (S)-6-methylheptan-2-ol [derived from transition state (6)], as expected from a consideration of the relative steric interactions. Transition state (5) has a less favourable Me—Me and Et—Hex interaction and hence a higher free energy of activation it therefore represents the less favourable reaction pathway (see p. 15). 

Side-chain Cleavage.—Doubt has been cast on the claim that in cholesterol (93) either C(20)—C(22) or C(17)—C(20) may be cleaved. Using [1,2-3H2,26- " C]-cholesterol, active isocaproic acid was obtained, but 6-methylheptan-2-one (94) was largely inactive and contained both tritium and The first-formed compound is probably the aldehyde (95), which is further metabolized to both isocaproic acid and 4-methylpentan-l-ol. ... 

Demole, E., C. Demole, and D. Berthet A chemical smdy of burley tobacco flavour Nicotiana tabacum L.). in. Structure determination and synthesis of 5-(4-meth-yl-2-furyl)-6-methylheptan-2-one ( solanofuran ) and of 3.4.7-trimethyl-l,6-dioxaspiro[4,5]dec-3-en-2-one ( spiroxabovolide ). Two new flavor components of burley tobacco Helv. Chim. Acta 56 (1973) 265-271. 

The two ethyl-homologous carbonyl compounds (286) and (289) have so far only been found in tea oil (49J). The possibility that 5-ethyl-6-methylheptan-2-one (286) originates from the metabolism of a monocyclic monoterpene cannot be excluded (49J), although this ketone seems more likely to be formed by oxidative biodegradation of the sitosterol side chain. Thus, for instance, all the aroma compounds (282) to (291) listed here except (286) and (289) were detected in tobacco oil (777, J42, 306, 463, 590). 

The prefixes for the —OH and —NH2 substituents are hydroxy and amino respectively. Thus, the name of molecule (b) is 5-hydroxy-6-methylheptan-2-one. 

Within Hymenoptera, pheromones produced by workers in social colonies are the best studied across many genera, principally in ants [6], with those eliciting trail following most extensively studied. The distinct behavior and the relative ease of the bioassay have resulted in chemical identifications in many species [ 113,114]. Those that have been recently identified are listed in Table 5. In addition, several alarm and recruitment signals have recently been identified. Many of the compounds recently identified in ants have previously been reported as trail or alarm pheromones in other ant species. For example, methyl 4-methylpyrrole-2-carboxylate 64, 3-ethyl-2,5-dimethylpyrazine 65, (9Z)-hexadec-9-enal 66,4-methylheptan-3-ol 67, and methyl 6-methylsalicy-late 68 have been identified as trail pheromone components, and heptan-2-one 69,4-methylheptan-3-one 70, formic acid 71, undecane 61,4-methylheptan-3-ol 67, methyl 6-methylsalicylate 68, and citronellal 72 have been identified as alarm pheromone components [6]. The use of the same chemicals across genera, with some used for very different functions, is an interesting phenomenon. 

Chiral columns are also employed in pheromone research for the determination of the absolute configuration of stereoisomers. The configuration of 4-methylheptan-3-ol and 4-methylheptan-3-one, sex pheromones of the oak bark beetle, were determined using a fused silica column coated with octakis [6-0-methyl-2,3-di-0-pentyl]-7-cyclodextrin. The elution order of the ketone stereoisomers was determined according to the literature and the natural compound was found to be (S)-methylheptanone. The absolute configuration of the alcohol present in the insects was determined by comparison with authentic standards and was found to be (3R, 4S)-methylheptanol. 

Fig. 1.6.1-2 gives an example of the scheme of elementary steps occurring in the thermal cracking of 3-methylheptane, just one of the 200-300 feed components to be considered in the modeling of naphtha-cracking. It is initiated by a yS-radical. Hydrogen atoms with different nature (primary, secondary) can be abstracted from such a molecule. The produced methyl-heptyl radicals can isomerize but also decompose by yS-scission into hexyl-radicals. The large olefins will further react by //-abstraction or radical-addition. 

Since there are two different connections possible for n-octane, 1,6 or 3, 8, which could lead eventually to ethylbenzene, there is a statistical entropy factor involved here which is not part of the o-xylene route. Therefore, if both closures were equally possible from an enthalpy perspective, one would predict a 2 1 ethylbenzene to o-xylene ratio. The formation of the m- and p-xylene requires prior isomerization of n-octane to 2- and 3-methylheptane, respectively. 

We have not carried out calculations starting with secondary cations derived from the title alkanes because at a computational level, these will have ground-states and transition-states similar to heptane itself (previously discussed). This will be true even though the most stable carbocations in these branched alkanes will be the corresponding tertiary ions, which in themselves will not be directly involved in dehydrocyclization processes. However, one has to keep in mind that the thermodynamic ground-states in these real catalytic reactions will be the alkanes themselves, and in this regard secondary cations formed from n-octane or 2- (or 3-) methylheptane will not differ much in absolute energy. As shown earlier, a 1,6-closure of 2-methylheptane leads eventually to m-xylene, while 3-methylheptane has eventual routes to both o- and p-xylene. 

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