Journal ArticleDOI
Why does cyclopropene have the acidity of an acetylene but the bond energy of methane
TLDR
It is noted that for simple hydrocarbons which give localized carbanions upon deprotonation there is an apparent linear correlation between any two of the following three quantities: deltaH degrees (acid), BDE, and EA.Abstract:
The gas-phase acidity of 3,3-dimethylcyclopropene (1) has been measured by bracketing and equilibrium techniques. Consistent with simple hybridization arguments, our value (deltaH degrees (acid) = 382.7 +/- 1.3 kcal mol(-)(1)) is indistinguishable from that for methylacetylene (i.e., deltadeltaH degrees (acid)(1 - CH(3)Ctbd1;CH) = 1.6 +/- 2.5 kcal mol(-)(1)). The electron affinity of 3,3-dimethylcyclopropenyl radical (1r) was also determined (EA = 37.6 +/- 3.5 kcal mol(-)(1)), and these quantities were combined in a thermodynamic cycle to afford the homolytic C-H bond dissociation energy. To our surprise, the latter quantity (107 +/- 4 kcal mol(-)(1)) is the same as that for methane, which cannot be explained in terms of the s-character in the C-H bonds. An orbital explanation (delocalization) is proposed to account for the extra stability of 1r. All of the results are supplemented with G3 and B3LYP computations, and both approaches are in good accord with the experimental values. We also note that for simple hydrocarbons which give localized carbanions upon deprotonation there is an apparent linear correlation between any two of the following three quantities: deltaH degrees (acid), BDE, and EA. This observation could be of considerable value in many diverse areas of chemistry.read more
Citations
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Transition metal chemistry of cyclopropenes and cyclopropanes.
Journal ArticleDOI
Theoretical Analysis of Factors Controlling Pd-Catalyzed Decarboxylative Coupling of Carboxylic Acids with Olefins
TL;DR: Mechanistic studies on decarboxylative coupling not only improve the understanding of the newly discovered transformations, but also may have valuable implications for the development of more effective catalyst systems.
Journal ArticleDOI
Gold(I)-catalyzed asymmetric cyclopropenation of internal alkynes.
John F. Briones,Huw M. L. Davies +1 more
TL;DR: Highly enantioselective cyclopropenation of internal alkynes with aryldiazoacetates was achieved using the binuclear gold catalyst (S)-xylylBINAP(AuCl)(2), activated by silver hexafluoroantimonate.
Journal ArticleDOI
Asymmetric Preparation of Polysubstituted Cyclopropanes Based on Direct Functionalization of Achiral Three-Membered Carbocycles
Longyang Dian,Ilan Marek +1 more
TL;DR: New methods for the synthesis of enantiomerically enriched cyclopropanes through catalytic and asymmetric direct functionalization of simple achiral three-membered carbocycle precursors are presented, allowing the preparation of a large variety of polysubstituted alkyl-, vinyl-, alkynyl-, and arylcyclopropanes.
Journal ArticleDOI
Nonconjugated Hydrocarbons as Rigid‐Linear Motifs: Isosteres for Material Sciences and Bioorganic and Medicinal Chemistry
TL;DR: This Review article focuses on covalently linked, nonconjugated linear arrangements and discusses the physical and chemical properties and differences of individual linkers, as well as their application in material and medicinal sciences.
References
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Gas-phase reactions of organic anions as studied by the flowing afterglow technique
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Scaling Factors for Obtaining Fundamental Vibrational Frequencies and Zero-Point Energies from HF/6–31G* and MP2/6–31G* Harmonic Frequencies
TL;DR: In this paper, the scaling factors for obtaining fundamental vibrational frequencies and zero-point vibrational energies from harmonic frequencies calculated at the HF/6−31G* and MP2/6-31G*) levels were derived from a comparison of a total of 1066 calculated frequencies for 122 molecules with corresponding experimental values.
Journal ArticleDOI
Estimation of heats of formation of organic compounds by additivity methods
N. Cohen,S. W. Benson +1 more
TL;DR: In this article, the authors take a kineticist perspective in answering the question, what is a ''sufficiently accurate`` prediction of an enthalpy of formation, i.e., the difference between, say, 90% and 64% reaction yield.