Hydrogen deficiency and heteroatoms

Normally, over 95% of total ions could be assigned probable formulae. Additional combinations did not explain any more of the data. Finally, the data was evaluated for usual patterns of ion peaks in any particular group. Typically, a series separated by 14 mass units(methylene) was seen in each group with a certain hydrogen deficiency and heteroatom content. 

Boduszynski, M.M. Composition of heavy petroleum. 1. Molecular weight, hydrogen deficiency, and heteroatom concentration as a function of atmospheric equivalent boihng point up to 100°F (160 C), Energy Fuels 1987, 7,2-11. 

The HRMS data were collected on a Kratos MS-50 operating with an El source at low eV with resolving power of 80,000 (batch tars) and at 70 eV with 50,000 resolution (in situ pyrolysis). The data was transferred to another computer system and analyzed using a program which we have developed. Initially, empirical formulae were assigned and deviations between calculated and observed masses determined. Next, peaks were sorted by heteroatom content, and finally by hydrogen deficiency (HD = rings... 

An examination of this table shows, however, that not only are coals hydrogen deficient, they also contain higher concentrations of heteroatoms (N, S and 0) than shale oil. Therefore, heteroatom removal comprises a large fraction of the hydrogen consumption, although not to the same extent as shale oil. 

Despite the significant developments in recent years, there is still much left to do in this chemistry, for instance, the types of hydride donors and acceptors are still rather limited. More C(sp )-H ot to heteroatoms, which have lone pairs, e.g., phosphorus, bromine, chlorine, etc., are likely to be exploited as hydrogen donors and more diverse electron-deficient species can be employed as hydrogen acceptors. 

The Homer - Emmons reagent (52) is effective in the one carbon homologation of ketones possessing acidic a-hydrogen atoms <96SL875> and electron-deficient alkenes add to 2-phenylseleno-l,3-dithiane in a photo-initiated heteroatom stabilised radical atom transfer process, giving products of considerable synthetic potential <96TL2743>. 

Hydroboration, the addition of a boron-hydrogen bond across an unsaturated moiety, was first discovered by H. C. Brown in 1956. Usually, the reaction does not require a catalyst, and the borane reagent, most commonly diborane (B2H6) or a borane adduct (BH3-THF), reacts rapidly at room temperature to afford, after oxidation, the /AMarkovnikov alkene hydration product. However, when the boron of the hydroborating agent is bonded to heteroatoms which lower the electron deficiency, as is the case in catecholborane (1,3,2-benzodioxaborole) 1 (Scheme 1), elevated temperatures are needed for hydroboration to occur.4 5... 

The effects of heteroatoms on autoxidation reactions are reviewed and discussed in terms of six phenomena (1) the effect on reactivity of a-hydrogens in the hydroperoxide chain mechanism in terms of electron supply and withdrawal (2) the effect on a-hydrogen acidity in base-catalyzed oxidation (3) the effect on radical ion stability in base-catalyzed redox chains (4) the possibility of heteroatom hydrogen bond attack and subsequent reactions of the resulting heteroradical (5) the possibility of radical attack on higher row elements via valence expansion (6) the possibility of radical addition to electron-deficient II and III group... 

As mentioned earlier, nucleophilic attack at ring carbon atoms a and y to a heteroatom is a reaction characteristic of the ir-deficient six-membered heterocycles. Within this context we do not regard hydrogen atoms attached to ring carbon atoms as substituent groups, and hence proton removal to generate a carbanionic centre is classified as a reaction at a ring carbon atom. There are thus six major reaction types, summarized in equations (21)—(26) in terms of the initial mechanistic steps. 

Fluorine can share three sets of lone-pair electrons with electron-deficient atoms intramo-lecularly or intermolecularly, in particular with a relatively acidic hydrogen bound to a heteroatom. In addition, as described in section 1.4, strongly electron-withdrawing per-fluoroalkyl groups increase the acidity of proximate functional groups such as alcohol, amine, amide, and carboxylic acid. 

The acidity of the hydrogen atoms at C-2 and C-4, as measured by hydrogen-deuterium exchange data, could not be correlated with Huckel MO, Pariser-Parr-Pople (PPP), or variable / ,y-PPP localization energies calculations. The deficiency of /S-electron methods was probably because of the field effects of the heteroatoms and their lone pairs of electrons. ... 

As described in Section 11.5.12 with reference to SnI reactions, a hydride or alkyl shift in a carbenium ion is a common rearrangement. It entails the movement of a hydrogen, alkyl, or vinyl / aryl group from a carbon adjacent to a carbenium ion to the electrophilic center in order to create a more stable carbenium ion. Many rearrangements have a similar migration as a key step, with the additional feature of a heteroatom on the p-carbon that stabilizes the newly formed electron deficient center (Eq. 11.46). Two prototype examples are the pinacol rearrangement and the benzilic acid rearrangement. 

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