2- Methylpentane, 43 Table

Using Table III in Ref. 68 (p. 692), calculate the expected product composition from the gas-phase photochemical chlorination and bromination of 3-methylpentane under conditions (excess hydrocarbon) in which only monohalogenation would occur. 

Referring first of all to the reactions over 0.2% platinum/alumina (Table V) the major features of the product distributions may be explained by a simple reaction via an adsorbed C5 cyclic intermediate. For instance, if reaction had proceeded entirely by this path, 2-methylpentane-2-13C would have yielded 3-methylpentane labeled 100% in the 3-position (instead of 73.4%) and would have yielded n-hexane labeled 100% in the 2-position (instead of 90.2%). Similarly, 3-methylpentane-2-I3C would have yielded a 2-methylpentane labeled 50% in the methyl substituent (instead of 42.6%), and would have yielded n-hexane labeled 50% in the 1- and 3-positions (instead of 43.8 and 49% respectively). The other expectations are very easily assessed in a similar manner. On the whole, the data of Table V lead to the conclusion that some 80% or so of the reacting hydrocarbon reacts via a simple one step process via an adsorbed C5 cyclic intermediate. The departures from the distribution expected for this simple process are accounted for by the occurrence of bond shift processes. It is necessary to propose that more than one process (adsorbed C6 cyclic intermediate or bond shift) may occur within a single overall residence period on the catalyst Gault s analysis leads to the need for a maximum of three. The number of possible combinations is large, but limitations are imposed by the nature of the observed product distributions. If we designate a bond shift process by B, and passage via an adsorbed Cs cyclic intermediate by C, the required reaction paths are... 

Unlike the behavior over 0.2% platinum/alumina, the main features of the labeled product distributions obtained over 10% platinum/alumina and over platinum film catalysts (Tables VI and VII respectively) cannot be explained in terms of a single dominant reaction pathway via an adsorbed C6 cyclic intermediate. Again, parallel, multiple-step reaction pathways are involved. The results from 2-methylpentane-2-13C have been qualitatively accounted for (84) by the pathways... 

Hexanc is a very volatile aliphatic hydrocarbon. It is a constituent in the paraffin fraction of crude oil and natural gas and is also used as an industrial chemical and laboratory reagent. Laboratory grade -hexane contains approximately 99% w-hexane. "Hexane" or "hexanes" is a commercial and industrial product consisting of a mixture of hydrocarbons with six carbon atoms and includes -hexane and its isomers 2-methylpentane and 3-methylpentane as well as small amounts of other hydrocarbons (Brugnone et al. 1991). Laboratory and industrial solvents such as "hexane" and petroleum ether contain -hexane from <0.1% to as much as 33% (Creaser et al. 1983). Information regarding the chemical identity of -hexane is located in Table 3-1. 

Table 3 Arrhenius and Eyring activation parameters for the debrominations of 2,3-dibromo-2-methylpentane (27) and 1,2-dibromodecane (29) with di-n-hexyltelluride (26) and tetra-n-butylammonium iodide...

In helium, all hexanes give benzene (Table IV) (97, 97a). Methylcyclo-pentzne and methylpentanes give similar benzene yields. No saturated isomers are detected, and the ring opening of methylcyclopentane is negligible. 

A monotonic decrease of benzene yield from methylpentanes is observed as a function of the hydrogen pressure over both metals (27a, 91a). The intermediates of bond shift type dehydroisomerization are likely to be unsaturated. This points to the McKervey-Rooney-Samman mechanism (55). This pathway obviously has a higher energy barrier over platinum than over palladium as compared with the aromatization of -hexane. This is reflected also by the similar aromatization selectivity (iS r) values of -hexane and methylpentanes over palladium (Table IV). 

Table 15.2 Crystallization conditions for DNA-protein complexes using 2-methylpentan-2,4-diol (MPD) as a precipitant... 

The data in Table 7 show that the selectivity for 2-oxygenated products in the oxidation of alkanes on TS-1 is somewhat higher than could be expected on statistical grounds. Only for 3-methylpentane, this selectivity becomes overcompensated by the higher reactivity of tertiary C-H compared to secondary C-H positions. This indicates that the first step of the oxidation, i.e. the formation of alcohols from alkanes is slightly regioselective. Within the ketone fraction, the selectivity for 2-ketones is even more pronounced, indicating that 2-alcohols are selectively oxidized to 2-ketones in the... 

The most important flavour compound in raw onions is thiopropanal-S-ox-ide, the lachrymatory factor [145,146]. Other important flavour compounds are 3,4-dimethyl-2,5-dioxo-2,5-dihydrothiophene and alkyl alkane thiosulfonates such as propyl methanethiosulfonate and propyl propanethiosulfonate with a distinct odour of freshly cut onions [35, 36, 147]. Various thiosulfinates that have a sharp and pungent odour may also contribute to the flavour of onions. These compounds, however, are rapidly decomposed to a mixture of alkyl and alkenyl monosulfides, disulfides and trisulfides (Scheme 7.3) of which dipropyl disulfide, methyl ( )-propenyl disulfide, propyl ( )-propenyl disulfide, dipropyl trisulfide and methyl propyl trisulfide are the most important contributors to the aroma of raw and cooked onions (Table 7.5, Fig. 7.6) [148-150]. Recently, 3-mercapto-2-methylpentan-l-ol was identified in raw and cooked onions eliciting intense meat broth, sweaty, onion and leek-like odours [142, 151]. 

Problem 4.26 Assign numbers, ranging from (1) for lowest to (3) for highest, to the boiling points of the following hexane isomers 2,2-dimelhylbutane, 3-methylpentane. and n-hexane. Do not consult any tables for data. <... 

The boiling point, refractive index, and density of the olefin derivative of any paraffin were shown, by use of Table III, to stand in the onier of their olefin type. Table X contains the engine data of the olefin derivatives of 2-methylpentane and 3-methylpentane, recorded in the order of their olefin type. No consistent relations between octane numbers or critical compression ratios are obvious—but the blending octane numbers of these branched olefins, as measured by both the research and Motor methods, do generally stand in the order of their type. Two olefins of type III form exceptions, the exceptions being in one case too high and in the other case too low. 

The pre-exponential factor A3 has been discussed (for RH == methane and cyclohexane) previously (22). For 2-methylpentane at 550°K., As 10 12 9 cc. molecule"1 sec."1, assuming free rotation in the transition state. Corresponding values for 2-methylpropane and ethane are 10 12 6 and 10"12 2 cc. molecule 1 sec. 1. The corresponding rate constants are given in Table II. 

Before that time, little was known about their UV spectra. Ando and coworkers extended our knowledge about this facet of organosilicon chemistry by photolysis of silyldia-zomethanes 4 in 3-methylpentane at 77 K yielding the expected silenes 519 (equation 2). The measured UV spectra together with previous results are summarized in Table 1. 

For comparative study, various silenes were isolated in 3-methylpentane matrix at 77 K by photolysis of the corresponding silyldiazo compounds and their ultraviolet spectra are measured. The results are summarized in Table 1. The introduction of trimethylsilyl group on carbon results in slight red shift compared with the parent silene (H2Si=CH2, 258 nm). As one might expect, considerable bathochromic shifts have been observed for conjugated silenes such as 6c, 6d and 2829,30. 

The operating conditions for tests using 2,2,4-trimethylpentane, 2,3-dimethylbutane, 2-methylpentane, and no solvent are presented in Table II. The product yields and properties are presented in Table III. 

The first asymmetric hydroformylation with platinum catalysts was carried out42 using NMDPP as the asymmetric ligand. An optical yield of 9% was obtained in the hydroformylation of 2-methyl-l-butene to 3-methylpentanal. Subsequently, different types of olefins were asymmetrically hydroformylated using a catalytic system formed from [(—)-DIOP]PtCl2 and SnCl2 2 H20 in situ 42,45) (Table 4). 

To illustrate this method of approach, results of three of the experiments by Corolleur et al. are shown in Tables XIII and XIV. In the examples selected here, a 13C-labeled 3-methylpentane and a labeled 2-methylpentane are reacted, in turn, and distribution of 13C is shown for the methylpentane products in Table XIII and for the n-hexane products in Table XIV. Distributions expected for a pure cyclic mechanism (C) and for a methyl shift (T) are indicated. Detailed discussion by the authors of abnormal products (i.e., those not predicted by the single-stage purely carbocyclic mechanism) led to the conclusion that these are formed on a second, less numerous, type of surface site by the action of which a succession of several rearrangements, according to a cyclic or a bond-shift mechanism, takes place. In Table XIV it can be seen that assumption of a simple skeletal rearrangement of the type... 

In compound A, the longest continuous chain is live carbon atoms long, and there are no multiple bonds, so this compound is named as a pentane (see Table 20.1). The carbon atom to which the methyl group (CH3—) is attached is identified with the number 2 because that carbon is the second from the nearer end of the chain. The name is 2-methylpentane. Note that the number 2 is an address and does not mean two methyl groups. 

Recently, AEDA and SHA-0 yielded 41 and 45 odor active compounds for Scheurebe and Gewurztraminer wines, respectively (P). Ethyl 2-methylbutyrate, ethyl isobutyrate, 2-phenylethanol, 3-methylbutanol, 3-hydroxy-4,5-dimethyl-2(5H)-furanone, 3-ethylphenol and one unknown compound, named wine lactone, showed high flavor dilution (FD)- factors (Table I) in Gewurztraminer and Scheurebe wines. 4-Mercapto-4-methylpentan-2-one belongs to the most potent odorants only in the variety Scheurebe whereas cis-rose oxide was perceived only in Gewurztraminer (Table I). 4-Mercapto-4-methylpentan-2-one was identified for the first time in Sauvignon blanc wines (JO). The unknown compound with coconut, woody and sweet odor quality, which has not yet been detected in wine or a food, was identified as 3a,4,5,7a-tetrahydro-3,6-dimethylbenzofuran-2(3H)-one (wine lactone) (JJ). 

To estimate the sensory contribution of the 42 odorants to the overall flavor of the wine samples, their OAV s were calculated (Table II). To take into account the influence of ethanol, the odor threshold values of wine odorants were determined in a mixture of water/ethanol (9+1, w/w) and were used to calculate the OAV s for each compound. According to the results in Table A, 4-mercapto-4-methylpentan-2-one, ethyl octanoate, ethyl hexanoate, 3-methylbutyl acetate, ethyl isobutyrate, (E)-fi-damascenone, linalool, cis rose oxide and wine lactone showed the highest OAV s in the Scheurebe wine. With exception of 4-mercapto-4-methylpentan-2-one the above mentioned odorants also showed the highest OAV s in Gewurztraminer wine. Differences in the OAV s of ethyl octanoate, ethyl hexanoate, 3-methylbutyl acetate and ethyl isobutyrate between the two varieties are probably caused by differences in the maturity of the fruit at harvest and/or by the fermentation process. 

Examination of the alkylperoxy radicals which may be formed from 3-ethylpentane, 3-methylpentane and 2-methylpentane shows that, in each case, some may undergo isomerization reactions with relatively low activation energies [58], examples of which are shown in Table 20. 

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