Butyl bromide, structure

Suggest a structure for the product of nucleophilic substitution obtained on solvolysis of tert-butyl bromide in methanol and outline a reason able mechanism for its formation... 

From Ingold, Structure and Mechanism in Organic Chemistry, 315. See Ingold, with L. C. Bateman, K. A. Cooper, and E. D. Hughes, "Mechanism of Substitution at a Saturated Carbon Atom. Pt. XIII. Mechanism Operative in the Hydrolysis of Methyl, Ethyl, Isopropyl, and Tert.-Butyl Bromides in Aqueous Solutions," JCS... 

Primary alkyl halide C HgBr (a) reacted with alcoholic KOH to give compound (b). Compound (b) is reacted with HBr to give (c) which is an isomer of (a). When (a) is reacted with sodium metal it gives compound (d), CgH g which is different from the compound formed when n-butyl bromide is reacted with sodium. Give the structural formula of (a) and write the equations for all the reactions. 

A structural isomer has been made, with the butyl group branched at the nitrogen atom. This is N-s-butyl-N-methyltryptamine, or MSBT. It came from a two pass alkylation of N-methyltryptamine (NMT) with s-butyl bromide in isopropylalcohol in the presence of solid potassium iodide. It remained an oil, but was over 90% pure by GCMS, with unreacted NMT being the major impurity. MS (in m/z) C6H14N+ 100 (100%) indolemethylene+ 130 (8%) parent ion 230 (1%). It has been assayed in man, but it remains an unknown. 

The results of the alkylation of 6 377a 426-427 429 are summarized in Table XI. In addition to the above factors, the regioselectivity of electrophilic attack on 518 was strongly affected by the structure of the alkylating agents, e.g., methyl iodide, ethyl bromide, cyclohexyl bromide, and rm-butyl bromide. 

Hydrodehalogenation. Unlike slurries of LiAlH4 in ethereal solvents, clear solutions of the hydride in THF reduce alkyl halides to the corresponding alkanes rapidly and often in practically quantitative yield.8 However at least 1 molar equiv. of LiA 1H4 per RX is required (equation I). The rate of reduction for the halides is I > Br>Cl. The effect of the structure on the rate is in the order n-butyl bromide >... 

A good way to work this problem is to start by writing structures for all compounds with the molecular formula C4H4Br. There are only four. The first compound must have nine equivalent hydrogens. The only possible structure is f-butyl bromide ... 

It was first suggested200,201 that the stabilized structure could be dependent upon the nature of the matrix, but irradiation of isobutyl bromide and /-butyl bromide in TMS or adamantane solutions at 77 K together with the temperature dependence of the resulting spectra led Symons and Smith202 to identify the species with the small Br coupling as the /-butyl radical bromide ion adduct Me3C —Br". 

A triple anion complex containing enolate, amide, and halide functionalities can be isolated from the mixture of n-butyl bromide, hexamethyldisilazane, TMEDA, Bu Li and pinacolone (Bu COMe). The resulting solution of LiBr, LiN(SiMc3)2, LiOC(Bu )=CH2, and TMEDA produces crystals of Li4(/.t4-Br)( u-OC(Bu )=CH2)2(M-N(SiMe3)2)(TMEDA)2, which, instead of forming a ladder-type structure, consists of a planar butterfly of four lithium atoms bonded to a //4-Br the stability of this arrangement has been studied with semi-empirical (PM3) and ab initio HE/ LANL2DZ computations. ... 

Problem 3.22 The final step in the proof of structure of an unknown alkane was its synthesis by the coupling of lithium di(rer/-butyl)copper w ith w-butyl bromide. What was the alkane ... 

We have proposed that, under the conditions we have described, methyl bromide reacts with hydroxide ion by the Sn2 mechanism, and that ferf-butyl bromide reacts by the SnI mechanism. Since 5ec-alkyl bromides are intermediate in structure between these two halides, it is not surprising to find that they can react by either or both mechanisms. 

Give the structures and names of the chief organic products expected from the reaction (if any) of -butyl bromide with ... 

Table 1 gives a qualitative comparison of the reactivities of a number of representative polar organometallics towards n-butyl bromide. From this table, working temperature ranges for preparative alkylations of structurally analogous polar organometallics can be derived. 

Working backwards, one can determine the structure of the other compounds. Only the alkyl halide t-butyl bromide could have reacted with AgOH to produce this tertiary alcohol ... 

You are given the product structures. Therefore your task is to identify the mechanistic pathway in each case How do you get there from here Use the information in Section 7-6. Use as a model the mechanism on page 266 for El reaction of 2-bromo-2-methylpropane (rm-butyl bromide) in methanol. 

For the preparation of MBM, the starting phenol was alkylated to 2-(n)-butoxy-1,4-dimethoxybenzene in methanolic KOH with n-butyl bromide. The benzaldehyde melted at 79.5-81 °C from methanol, and formed a malononitrile derivative that had a melting point of 134.5-135 C. The nitrostyrene from the aldehyde and nitroethane in acetic acid crystallized from methanol with a mp of 71-72 °C. Lithium aluminum hydride reduction in ether gave the ether-insoluble chloroform-soluble product 4-(n)-butoxy-2,5-dimethoxyamphetamine hydrochloride (MBM) with a melting point of 128-130 °C. This product met all tests for structural integrity, and assays were started. At levels of up to 12.0 milligrams, there were no effects noted. 

None of these compounds has structural features necessary to promote SnI (not even the third notice that the bromine is attached to a primary carbon, even though there is a tert-butyl group in the molecule), so we need to think about Sn2 reactivity only. In general, steric hindrance slows dovm Sn2 reactions, so we can start by saying that methyl bromide > -butyl bromide > cyclohexyl bromide. But how do the other two fit into the scale An adjacent carbonyl group accelerates Sn2 reactions enormously, so the ketone will react even faster than methyl bromide. On the other hand, a bulky tert-butyl group adjacent to a reaction centre leads to very slow substitution, so this compound ( neopentyl bromide ) goes at the bottom of the scale. 

Finally, despite use of solvents (or mixtures of solvents) to solvate the intermediate carbocation and the anion, the structure of the substrate continues to play the criticalrole and,for example,while,as noted above,at50°C,2-bromo-2-methylpropane (f-butyl bromide [(CH3)3C-Brj) dissociates approximately 105 times faster than 2-bromopropane (isopropyl bromide [(CH3)2CHBrj) in water at 50°C, the difference is only slightly diminished (from 105 to 104) in 60% ethanol 40% water (v/v) at 55°C. 

PROBLEM 7.15 Although fer/-butyl bromide does not give tert-h xty alcohol on reaction with hydroxide ion, an alkene product (C4H8) is produced. Suggest a structure for the product and an arrow formalism for this bimolecular reaction. 

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