Bond Energy Terms Research Articles

Mass spectral studies of organoboron compounds. Part I. Facility of hydrocarbon ion rearrangements in some phenylborolans under electron impact

The mass spectra of phenyldioxa-, phenyloxathia-, and phenyldithia-borolans have been examined and a full analysis is reported. The formation of hydrocarbon ions, by electron impact-induced rearrangement, from these heterocycles is rationalised in terms of the relative bond-energies between the atoms in the heterocyclic ring.

Bonding studies of compounds of boron and the group IV elements. Part VIII. Heats of hydrolysis and bond energies for some trimethylmetalyl derivatives Me3M–X(M = Si, Ge, and Sn)

The heats of hydrolysis, in aqueous 1 M-hydrochloric acid, of one silicon, five germanium, and eight tin(IV) compounds of type (Me3M)nX (where M = Si, Ge, or Sn, n= 1–3, and X is a univalent ligand in which the donor atom adjacent to M is N, O, S, Cl, Br, or I) to give (Me3Si)2O, (Me3Ge)2O, and (Me3SnOH)2 have been measured. From these, standard heats of formation have been calculated as follows: ΔHf°(Me3Si·OEt), I =–126·4 ± 0·7; ΔHf°[(Me3Ge)2O], I =–136·0 ± 4·0; ΔHf°(Me3GeCl), I =–71·6 ± 2·1; ΔHf°(Me3GeBr), I =–62·1 ± 2·1; ΔHf°(Me3Ge·OEt), I =–95·8 ± 2·2; ΔHf°(Me3Ge·SBun), I =–64·7 ± 2·1; ΔHf°(Me3Ge·NMe2), I =–37·1 ± 2·2; ΔHf°(Me3SnCl), c =–58·4 ± 1·2; ΔHf°(Me3SnBr), c =–48·8 ± 1·3; ΔHf°(Me3SnI), I =–31·2 ± 1·1; ΔHf°(Me3SnOH), c =–90·8 ± 1·2; ΔHf°(Me3Sn·OEt), I =–73·1 ± 1·5; ΔHf°(Me3Sn·SBun), I =–47·1 ± 1·6; ΔHf°(Me3Sn·NMe2), I =–13·3 ± 1·4; ΔHf°[(Me3Sn)2NMe], I =–31·5 ± 2·5; ΔHf°[(Me3Sn)3N], c =–29·2 ± 3·6 kcal mol–1. Gas-phase enthalpies of formation of these compounds and thermochemical bond energy terms E(M–X) have been calculated. Group trends show that, for constant X, E(C–X) E(Ge–X) > E(Sn–X), whereas E(C–Y) > E(Si–Y)(Y = H or Me). Another conclusion is that the ‘softness’(in terms of ΔH of reactions) of the acid Me3M+ increase in the order C < Si < Ge < Sn; several chemical reaction types are examined in this light.

Bond energy terms for methylsilanes and methylchlorosilanes

Bond energy terms for methylsilanes and methylchlorosilanes

Bonding studies of compounds of boron and the group IV element : VI. Mas spectrometric studies on compounds Me 4M and Me 3MM′Me 3 (M and M′ = C, Si, Ge, Sn, and Pb): thermochemical data

The mass spectra of the series of compounds Me 3MM′Me 3 and Me 4M are reported and analysed, where M and Mt́ are C, Si, Ge, Sn, and Pb. Ionisation potentials of the parent molecular ions and appearance potentials of Me 3M + and Me 3M′ + fragment ions have been measured. Using known or estimated values for the gas phase standard enthalpies [Δ H o f (g)] of formation of Me −, Me 3C −, Me 3C +, Me 4M, Me 6C 2, Me 6Si 2, and Me 6Sn 2 yields an overdetermined set of 31 simultaneous equations for the Δ H o f (g) of 27 molecules, radicals, and ions. A least squares analysis thus affords the Δ H o f (g) data for all the species Me 3MM′Me 3, Me 4M, Me 3M −, and Me 3M +. From these data, values are derived for bond ( D) and mean bond ( D ) dissociation energies: D(Me 3MMe), D(Me 3MM′Me 3), and D (Me 4M), as well as meant hermochemical bond energy terms ( E ) for MeM and MMt́ bonds in each of these species. Data (in kcal/mole) include ( i). E (MeM) in Me 4M (value for M in parentheses): 82.1(c), 68.5(Si), 59.9(Ge), 48.1(Sn), and 32.9(Pb); ( ii). E(MM′) in Me 6M 2 : 78.9(c), 68.0(Si), 59.3(Ge), 38.3(Sn), and 33.3(Pb); ( iii). E(MC) in Me 3MCMe 3 : 66.6(Ge), 53.0(Sn), and 41.6(Pb); ( iv). E(MSi) in Me 3MSiMe 3 : 63.3(Ge) and 56.1(Sn), and ( v). E(GeSn) in Me 3GeSnMe 3 : 53.7. Trends are discussed.

Thermochemical studies on the halogenation of tetraphenyllead

Abstract The bromination and iodination of tetraphenyllead and the corresponding triphenyllead halides have been studied in a solution calorimeter and the enthalpies of formation of the crystalline solids Ph3PbBr, Ph2PbBr2, Ph3PbI, and Ph2PbI2 have been derived. Values for the gas phase have been calculated using enthalpies of sublimation derived from vapourpressure measurements. The PbBr and PbI bond energy terms have been derived.

Standard heats of formation of two tribromoborazines

The heats of hydrolysis of B3Br3N3Me3 and B3Br3N3H3 are −84.4 ± 0.5 and −120.9 ± 0.5 kcal mole−1, and their standard heats of formation are −246.5 and −215.9 kcal mole−1, respectively. The estimated boron–nitrogen bond energy terms are 113.2 and 105.5 kcal mole−1, respectively.

The effect of bond energetics on determining the facility of tropylium ion formation from some phenylborolanes under electron impact

The electron impact-induced re-arrangement to form the tropylium ion from phenylborolanes containing oxygen and/or sulphur as the hetero-atoms is rationalised in terms of the relative bond energies between the atoms in the heterocyclic ring.

Organometallic compounds. V. Mass spectra of some aryltrimethyltins

AbstractThe mass spectra of a series of aryltrimethyltins are described and analysed. The main features are: a relatively weak molecular ion, a very important ArSnMe2+ ion (base peak), a low intensity ArSnMe+ fragment and a non negligible ArSn+ peak. These findings may be related to the well known stable valence states of tin (IVSn and IISn) and the unfavourable IIISn and ISn states. Whereas a methyl group is easier to cleave from the ArSnMe3+ ion than the phenyl radical, n‐butyl seems to be more strongly bound to the metal than the aryl moiety in ArSnnBu3+.The spectra of three aryltrimethylsilicons, recorded in the same conditions, show stronger molecular ions and weaker divalent fragments than in the corresponding tin derivatives.An interpretation of these various findings is attempted in terms of bond energies and electron delocalization.

Bond energy formulations of heterogeneous nucleation theory

Condensation of a vapour beam on s substrate depends on the formation and growth of stable nuclei. By expressing the volume and surface energies of the capillarity model and also the cluster energies of the atomistic model in terms of nearest-neighbour bond energies, these two approaches to nucleation theory have been put into forms which may be directly compared. This has revealed that their differences are confined to: (i) continuous and discontinuous variation of critical sizes; (ii) a numerical difference in the value of supersaturation for small nuclei which has the effect in the capillarity model of predicting a larger size for the critical nucleus and a lower nucleation rate; (iii) a compensating numerical difference which is revealed in a comparison of cluster energies, using the bond energy formulation, in which the idealized shapes of the capillarity model give higher cluster energies, smaller critical nuclei and a higher nucleation rate. It is shown that under nucleation conditions the capture rate of single atoms is independent of the sizes of the growing nuclei. In practical cases the critical nucleus is seldom larger than two atoms, and the atomistic model is preferred. Calculated values of nucleation rate are given in terms of incidence rate, substrate temperature, condensate bond strength and adsorption energy. The analysis of experimental data to derive material constants is discussed.

Enthalpies of Formation and Bond Energies of Some Fluoramines

From measurements of the enthalpies of explosion, the enthalpies of formation in kilocalories per mole of some fully fluorinated amines in the gas state were derived: F2C(NF2)2, −108.7; FC(NF2)3, −47.7; C(NF2)4, 0.5; FNC(NF2)2, 23.0; (F2N)2 CFNFCF(NF2)2, −84.4. The deviation of these values from those calculated from standard bond-energy terms is discussed.

The heats of hydrolysis of borazole and some derivatives

The heats of hydrolysis of N-trimethylborazole, borazole, B-trichloro-N-trimethylborazole, and B-trichloroborazole in water at 25° have been measured. The standard heats of formation are –231·9, –204·9, –263·5, and –256·3 kcal./mole, respectively, and the boron–nitrogen bond energy terms are 124·1, 117·9, 108·5, and 104·8 kcal./mole, respectively.

Thermochemistry of metal alkoxides. Part 3.—Heats of formation of vanadium tetratertiarybutoxide and chromium tetratertiarybutoxide

The standard heats of formation of vanadium and chromium tetratert.-butoxides have been determined by means of reaction calorimetry. Values for ΔH°f[M(OC4H9-tert.)4, g] were derived: Ti, –395; V, –328; Cr, –305 kcal/mole, and discussed in terms of average bond dissociation energies text-decoration:overlineD(M—O) and bond energy terms text-decoration:overlineE(M—O). The order of decreasing bond strengths Ti—O>V—O>Cr—O was discussed in terms of the increasing electronegativity of the metal xTi< xV(IV)< xCr(IV). The strengths of Ti—F, Ti—O and Ti—N bonds were compared and discussed in terms of electronegativities.

Thermochemistry of metal alkoxides. Part 2.—Heats of formation of some titanium alkoxides

Measurements of the heats of alcoholysis of titanium tetraethoxide in cyclohexane have been used to determine the standard heats of formation of various titanium tetra-alkoxides ΔH°f[Ti(OR)4, liq.], where R= n-C3H7, isoC3H7, n-C4H9, sec.-C4H9, n-C5H11 and tert.-C5H11. The values for Ti(OC4H9-n)4 and Ti(OC5H11-tert.)4 were checked by measurements of heats of reaction of the alcohols with titanium tetradiethylamide. The data were used to derive values for ΔH°f[Ti(OR)4, g], D(Ti—O) the average bond dissociation energy and E(Ti—O) the bond energy terms for Ti—O bonds. From the value of ΔH°f{Ti[N(C2H5)2]4, liq.}=–100 kcal/mole it was calculated that D(Ti—N)∼73 kcal/mole.

Boron–Nitrogen Bond Strengths in Borazoles

THE bond order of boron–nitrogen compounds and the aromatic character of borazoles have been subjects of interest for many years (see, for example, ref. 1). It is shown here that bond energy terms and bond length measurements give apparently conflicting information about the relative strengths of some boron–nitrogen bonds.

A bond energy scheme—II : Strain and conjugation energies in cyclic compounds

Strain energies in certain cyclic compounds, and conjugation energies in other cyclic compounds with delocalized π-electron systems are estimated with the aid of bond energy terms, of which some have been published and some are derived in the paper. The magnitudes of the strain energies found can in general be understood in terms of likely angular or torsional strain. The magnitudes of the conjugation energies found are appreciably lower than some previous estimates of these energies; attention is drawn to the uncertainties which remain in the calculation of conjugation energies from thermochemical data.

Bond-energy term values in hydrocarbons and related compounds

Bond-energy term values in hydrocarbons and related compounds

A bond energy scheme for aliphatic and benzenoid compounds

A bond energy scheme, valid for 25°C, has been developed from the premise that the energy of a CX bond depends on the hybridization state of the carbon atom. Bond energy terms for CX bonds in both aliphatic and benzenoid compounds have been derived for X fluoro, chloro, bromo, iodo, hydroxyl, oxide (ethers and adols), carbonyl, carboxyl, thiol, sulphide, sulphoxide, sulphone, primary-amino, or cyano. The heats of formation of many compounds have been calculated from the bond energy terms, and are tabulated and compared with experimentally determined heats of formation; discrepancies greater than 2 kcal/mole are few and are discussed separately. It is shown that by use of appropriate CC bond energy terms in carbonyl, carboxyl and cyano compounds, and of next-nearest-neighbour corrections in alcohols and ethers, all the bond energy terms are transferable from one compound type to another and that the magnitudes of the bond energy terms are compatible with known lengths of the bonds.

Heats of Combustion and Formation of Lower Members of Methyl-and Etnyl-methoxypolysiloxanes

Abstract 1. The heats of combustion of lower members of methyl- and ethyl-methoxy-polysiloxanes have been measured at 20°C and constant volume, and the corresponding heats of combustion and formation in isobaric process have been calculated. 2. The bond energy term in structural unit of (Remark: Graphics omitted.) has been calculated from the heat of formation, and it has been found that its value increases with the polymer sizes of the members. Finally, the (Remark: Graphics omitted.) has been compared with that expected from the additive law of bond energy, and the lowering of bond energy in these molecules has been discussed in view of the resonance effect.

281. Heats of combustion and molecular structure. Part V. The mean bond energy term for the C–O bond in ethers, and the structures of some cyclic ethers

281. Heats of combustion and molecular structure. Part V. The mean bond energy term for the C–O bond in ethers, and the structures of some cyclic ethers

Thermochemical Investigation on Organic Sulfur Compounds. IV. Thermochemical Sulfur Bond Energy Terms.

Thermochemical Investigation on Organic Sulfur Compounds. IV. Thermochemical Sulfur Bond Energy Terms.