The Conjugation Stabilization of 1,3-Butadiyne Is Zero

Rogers, Donald W.; Matsunaga, Nikita; Zavitsas, Andreas A.; McLafferty, Frank J.; Liebman, Joel F.

doi:10.1021/ol030019h

Cited by 66 publications

(51 citation statements)

References 25 publications

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“…An example of a hypohomodesmotic equation is given below, which (like the isodesmic BSE reaction above) has been used, in an equivalent way, to evaluate the diyne conjugation energy. [44,45] HCC…”

Section: Resultsmentioning

confidence: 99%

“…[45] In our view, such equations are inappropriate to evaluate conjugative stabilization, [13] as hyperconjugation is present in the reference olefins (and acetylenes) on the left side but is not compensated on the right. Furthermore, both 1-butene and 1-butyne (used in Equations (7) and (8) as reference molecules) also contain a single protobranching interaction.…”

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confidence: 99%

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The Concept of Protobranching and Its Many Paradigm Shifting Implications for Energy Evaluations

Wodrich

Wannere

et al. 2007

Chemistry A European J

189

203

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Branched alkanes like isobutane and neopentane are more stable than their straight chain isomers, n-butane and n-pentane (by 2 and 5 kcal mol(-1), respectively). Electron correlation is largely responsible. Branched alkanes have a greater number of net attractive 1,3-alkyl-alkyl group interactions, there are three such stabilizing 1,3 "protobranching" dispositions in isobutane, but only two in n-butane. Neopentane has six protobranches but n-pentane only three. Propane has one protobranch and is stabilized appreciably, by 2.8 kcal mol(-1), relative to methane and ethane. This value per protobranch also applies to the n-alkanes and cyclohexane. Consequently, energy evaluations employing alkane reference standards, for example, of small ring strain and stabilizations due to conjugation, hyperconjugation, and aromaticity, should be corrected for protobranching, for example, by employing Pople's isodesmic bond separation reaction method. This reduces the ring strain of cyclopropane to 19.2 from the conventional 27.7 kcal mol(-1), while the stabilization energies of alkenes and alkynes due to hyperconjugation (5.5 and 7.7 kcal mol(-1) for propene and propyne) and conjugation (14.8 and 27.1 kcal mol(-1) for butadiene and butadiyne) are considerably larger than the traditional estimates. Widely diverging literature evaluations of benzene resonance energy all give approximately 65 kcal mol(-1) after adjusting for conjugation, hyperconjugation, and protobranching "contaminations." The BLW (block localized wavefunction) method, which localizes pi bonds and precludes their interactions, largely confirms these stabilization estimates for hyperconjugation, conjugation, and aromaticity. Protobranching is seriously underestimated by theoretical computations at the HF and most DFT levels, which do not account for electron correlation satisfactorily. Such levels give bond separation energies, which can differ greatly from experimental values.

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Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

The Concept of Protobranching and Its Many Paradigm Shifting Implications for Energy Evaluations

Wodrich

Wannere

et al. 2007

Chemistry A European J

189

203

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“…Strong donor/acceptor groups usually lead to efficient transfer, such as HOMO-LUMO transitions, and fluorescence is subsequently quenched in relatively polar solvents. [15] Fluorescence intensity profiles for all the samples fitted to bi-exponential decays.…”

Section: Linear Optical Propertiesmentioning

confidence: 99%

Heteroaromatic Cation‐Based Chromophores: Synthesis and Nonlinear Optical Properties of Alkynylazinium Salts

et al. 2010

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“…In that Ref. [18] tells us that butadiyne lacks conjugation enthalpy (in contradistinction to butadiene), perhaps we should not be surprised at the lack of conjugation enthalpy in this species-however, the degree of destabilization is nonetheless a surprise.…”

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confidence: 98%

“…We may ask what is the conjugation enthalpy of two triple bonds. Parallelling the analysis in [18], we would naturally compare the enthalpies of the following reactions and then define the conjugation energy as the difference between the values of twice the first reaction and the second.…”

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Paradigms and paradoxes: organic thermochemistry without hydrogen: carbon oxides and nitrides

Slayden

Liebman

2008

Struct Chem

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All organic compounds contain carbon. Most contain hydrogen. This brief study discusses the enthalpy of formation of a collection of organic compounds containing only oxygen or nitrogen accompanying the carbon.By definition, organic chemistry is the chemistry of carboncontaining compounds. Almost always, in practice organic chemistry is also the chemistry of compounds containing hydrogen. Relatedly, organic thermochemistry discusses the thermochemistry of carbon-, and most often, hydrogen-, containing species. There are several thousand organic species for which the enthalpies of formation is known. In the current note we discuss the enthalpies of formation of those species that lack hydrogen, in particular, carbon oxides and carbon nitrides but not halocarbons. The current study will be limited to those species for which these data are found from experiment, whether or not the species be isolable. We will also limit our attention to neutral species and so ignore all ions such as the commonplace CN -and rather exotic CN + . We proceed first through the oxides and then the nitrides of carbon. Within each group, the compounds are discussed in order of increasing number of carbons, and then by increasing number of oxygens or nitrogens. All unreferenced enthalpies of formation in the current study are taken from Ref.[1] and may tacitly be assumed to refer to gaseous species at 298 K and 1 atm unless otherwise said.While there are a respectable number of species containing only carbon and oxygen, there are only three isolable compounds for which enthalpy of formation data are available: carbon monoxide (CO), carbon dioxide (CO 2 ) and propadienedione (C 3 O 2 ), the so-called carbon suboxide. Not limiting our species of interest by grounds of isolability allows us to consider other oxides of carbon, CO 3 , C 2 O, and C 3 O.Enthalpies of formation of CO and CO 2 are found from numerous sources. We choose the values -110.525 and -393.509 kJ/mol [2]. These values are well-established, the latter providing a benchmark value for the enthalpies of formation and combustion of nearly all organic compounds. Perhaps the only thermochemical observation of consequence we will make in this study relates to their carbon-oxygen bond energies. The ratio of the C-O bond energy in CO 2 to that of (the mean) value for CO is very nearly the same as the ratio for the Si-O bond energies in SiO 2 and gaseous SiO despite the fact that CO 2 is ''naturally'' a gas while SiO 2 is ''naturally'' a solid. Perhaps this is not so strange: this near constant ratio in the gas phase for some other pairs of species containing group 14-16 atoms was first pointed out in Ref. [3], and extended by consideration of experimentally unexplored neutrals [4] as well as valence isoelectronic pairs of cations [5], anions [5], and some hydrogen-containing pentatomics as well [6]. Summarizing, for 10 valence electron AB and 16 valence electron AB 2 , we findThis is a comfortably simple approximation for bond energies and a good example of how the investigation of

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The Conjugation Stabilization of 1,3-Butadiyne Is Zero

Cited by 66 publications

References 25 publications

The Concept of Protobranching and Its Many Paradigm Shifting Implications for Energy Evaluations

The Concept of Protobranching and Its Many Paradigm Shifting Implications for Energy Evaluations

Heteroaromatic Cation‐Based Chromophores: Synthesis and Nonlinear Optical Properties of Alkynylazinium Salts

Paradigms and paradoxes: organic thermochemistry without hydrogen: carbon oxides and nitrides

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