Relative reactivity of peracids versus dioxiranes (DMDO and TFDO) in the epoxidation of alkenes. A combined experimental and theoretical analysis

Comparative analysis of the calculated gas-phase activation barriers (DeltaE++) for the epoxidation of ethylene with dimethyldioxirane (DMDO) and peroxyformic acid (PFA) [15.2 and 16.4 kcal/mol at QCISD(T)// QCISD/6-31+G(d,p)] and E-2-butene [14.3 and 13.2 kcal/mol at QCISD(T)/6-31G(d)//B3LYP/6-311+G(3df,2p)] suggests similar oxygen atom donor capacities for both oxidants. Competition experiments in CH(2)Cl(2) solvent reveal that DMDO reacts with cyclohexene much faster than peracetic acid/acetic acid under scrupulously dried conditions. The rate of DMDO epoxidation is catalyzed by acetic acid with a reduction in the classical activation barrier of 8 kcal/mol. In many cases, the observed increase in the rate for DMDO epoxidation in solution may be attributed to well-established solvent and hydrogen-bonding effects. This predicted epoxidative reactivity for DMDO is not consistent with what has generally been presumed for a highly strained cyclic peroxide. The strain energy (SE) of DMDO has been reassessed and its moderated value (about 11 kcal/mol) is now more consistent with its inherent gas-phase reactivity toward alkenes in the epoxidation reaction. The unusual thermodynamic stability of DMDO is largely a consequence of the combined geminal dimethyl- and dioxa-substitution effects and unusually strong C-H and C-CH(3) bonds. Methyl(trifluoromethyl)dioxirane (TFDO) exhibits much lower calculated activation barriers than DMDO in the epoxidation reaction (the average DeltaDeltaE++ values are about 7.5 kcal/mol). The rate increase relative to DMDO of approximately 10(5), while consistent with the higher strain energy for TFDO (SE approximately 19 kcal/mol) is attributed largely to the inductive effect of the CF(3) group. We have also examined the effect of alkene strain on the rate of epoxidation with PFA. The epoxidation barriers are only slightly higher for the strained alkenes cyclopropene (DeltaE++ = 14.5 kcal/mol) and cyclobutene (DeltaE++ = 13.7 kcal/mol) than for cyclopentene (DeltaE++ = 12.1 kcal/mol), reflecting the fact there is little relief of strain in the transition state. Alkenes strained by twist or pi-bond torsion do exhibit much lower activation barriers.     

The effect of substitutents on the strain energies of small ring compounds

The effect of substitutents on the strain energy (SE) of cyclic molecules is examined at the CBS, G2, and G2(MP2) levels of theory. Alkyl substitutents have a meaningful effect upon the SE of small ring compounds. gem-Dimethyl substitution lowers the strain energy of cyclopropanes, cyclobutanes, epoxides, and dimethyldioxirane (DMDO) by 6-10 kcal/mol relative to an unbranched acyclic reference molecule. The choice of the reference compound is especially important for geminal electronegative substitutents. The SE of 1,1-difluorocyclopropane is estimated to be 20.5 kcal/mol relative to acyclic reference molecule 1,3-difluoropropane but is 40.7 kcal/mol with respect to the thermodynamically more stable (DeltaE = -20.2 kcal/mol) isomeric reference compound 2,2-difluoropropane. The SE of dioxirane (DO) is estimated to be approximately 18 kcal/mol while the SE of DMDO is predicted to be approximately equal to 11 kcal/mol by using homodesmotic reactions that maintain a balanced group equivalency. The total energy (CBS-APNO) of DMDO is 2.6 kcal/mol lower than that of isomeric 1,2-dioxacyclopentane that has an estimated SE of 5 kcal/mol. The thermodynamic stability of DMDO is a consequence of its relatively strong C-H (BDE = 102.7 kcal/mol) and C-CH(3) (BDE = 98.9 kcal/mol) bonds. By comparison, the calculated sec-C-H and -C-CH(3) G2 bond dissociation energies in propane are 100.3 and 90.5 kcal/mol.     

Effect of geminal substitution on the strain energy of dioxiranes. Origin of the low ring strain of dimethyldioxirane

The strain energies (SE) for dioxirane (DO) dimethyldioxirane (DMDO) and related dioxiranes have been examined by several methods using high-level computational schemes (G2, G2(MP2), CBS-Q). A series of calculated O-O, C-O, and O-H bond dissociation energies (G2) point to special problems associated with classical homodesmotic reactions involving peroxides. The relative SEs of DO, DMDO, methyl(trifluoromethyl)dioxirane (TFDO), and difluorodioxirane (DFDO) have been estimated by combination of the dioxirane with cyclopropane to form the corresponding 1,3-dioxacyclohexane. The relative SE predicted for DMDO (2) is 7 kcal/mol lower than that of DO, while the SE of 1,1-difluorodioxirane (4) is 8 kcal/mol higher. The most reactive dioxirane, methyl (trifluoromethyl)dioxirane (3), has an estimated SE just 1 kcal/mol greater than that of DO but 8 kcal/mol greater than that of DMDO. Six independent methods support the proposed SE for DO of 18 kcal/mol. The SE of the parent dioxirane (DO) has been estimated relative to six-membered ring reference compounds by dimerization of dioxirane and or its combination with cyclopropane. The relative SE of cyclic hydrocarbons, ethers and peroxides have been predicted by the insertion/extrusion of -CH(2)- and -O- fragments into their respective lower and next higher homologues. The moderated SE of DMDO (approximately equal to 11 kcal/mol) has also been estimated on the basis of group equivalent reactions. The unusual thermodynamic stability of DMDO is largely a consequence of combined geminal dimethyl and dioxa substitution effects and its associated strong C-H bonds and C-CH(3) bonds. The data clearly demonstrate that the reference compounds used to estimate the SE for highly substituted small ring cyclic compounds should reflect their molecular architecture having the same substitutents on carbon.     

The effect of carbonyl substitution on the strain energy of small ring compounds and their six-member ring reference compounds

High level ab initio calculations have been applied to the estimation of ring strain energies (SE) of a series of three- and six-member ring compounds. The SE of cyclohexane has been estimated to be 2.2 kcal/mol at the CBS-APNO level of theory. The SE of cyclopropane has been increased to 28.6 kcal/mol after correction for the one-half of the SE of cyclohexane. The SEs of a series of carbonyl-containing three-member ring compounds have been estimated at the CBS-Q level by their combination with cyclopropane to produce a six-member ring reference compound. The SEs of cyclopropanone (5), the simplest alpha-lactone (6) [oxiranone], and alpha-lactam (7) [aziridinone] have been predicted to be 49, 47, and 55 kcal/mol, respectively, after correction for the SE of the corresponding six-member ring reference compound. The SEs of cyclohexanone, delta-valerolactone, and delta-valerolactam have been estimated to be 4.3, 11.3, and 5.1 kcal/mol, respectively. Marked increases in the SE of silacyclopropane and siladioxirane have been established, while significant decreases in the SEs of phosphorus, sulfur, dioxa- and diaza-containing three-member ring compounds were observed. The ring strain energies of the hydrocarbons (but not heterocycles) exhibit a strong correlation with their C-H bond dissociation energies.     

The potential energy surface of singlet cyclobutadiene and substituted analogs: a coupled-cluster study

Coupled-cluster investigations (CCSD/cc-pVDZ and CCSD/cc-pVQZ//CCSD/cc-pVDZ) of singlet cyclobutadiene and fifteen-substituted analogs were conducted. A local minimum with a square frame does not exist on their potential surfaces. The well-known rectangular D_2h minimum, the square D_4h transition state, and two additional stationary points were found on cyclobutadiene’s potential surface. This included a transition state with a rhombic carbon ring and C_2h symmetry, separating two equivalent puckered C_2v local minima. The predicted barriers were 19.7 and 19.8 kcal/mol at the CCSD/cc-pVDZ and CCSD/cc-pVQZ//CCSD/cc-pVDZ levels, respectively. The relative strain energies of rectangular D_2h cyclobutadiene and all fifteen-substituted analogs were obtained from isodesmic reactions. Progressive substitution with methyl or BH₂ groups continuously lowers ring strain while increasing substitution with fluorines or trifluoromethyl groups steadily increases ring strain. C₄(BH₂)₄ is 16.6 and 13.3 kcal/mol less strained than cyclobutadiene while C₄F₄ is 17.7 and 21.5 kcal/mol more strained at the levels above. Cyclobutadiene is more strained than both cyclopropene and cyclobutene by 12.2 and 37.0 kcal/mol, respectively. Electron density contours indicate that fluorine substitution raised the electron density especially in the short C=C ring bonds above/below the ring plane (π-electrons) but not in the ring plane (σ-electrons). BH₂-substitutions lower the ring π-electron density with little effect in the ring plane. Methyl substituents have little effect on electron densities. All rings retain a strong bond alternation tendency (rectangular) whether substituted with electron-donating or -attracting groups. One-bond coupling constants and the percent p-character in ring C-to-C and C-to-substituent bonds are described.     

AM1 calculations of bond dissociation energies. Allylic and benzylic C-H bonds

AM1 method and correlation dependence between electronic relaxation energy and valence change on the C atom of the breaking bond were used to calculate the bond dissociation energies in 50 compounds with allylic or benzylic C-H bonds. The average calculation error is 0.8 kcal/mol.     

Energetic differences between the five- and six-membered ring hydrocarbons: strain energies in the parent and radical molecules

The C-H bond dissociation enthalpies (BDEs) for the five- and six-membered ring alkanes, alkenes, and dienes were investigated and discussed in terms of conventional strain energies (SEs). New determinations are reported for cyclopentane and cyclohexane by time-resolved photoacoustic calorimetry and quantum chemistry methods. The C-H BDEs for the alkenes yielding the alkyl radicals cyclopenten-4-yl and cyclohexen-4-yl and the alpha-C-H BDE in cyclopentene were also calculated. The s-homodesmotic model was used to determine SEs for both the parent molecules and the radicals. When the appropriate s-homodesmotic model is chosen, the obtained SEs are in good agreement with the ones derived from group additivity schemes. The different BDEs in the title molecules are explained by the calculated SEs in the parent molecules and their radicals: (1) BDEs leading to alkyl radicals are ca. 10 kJ mol (-1) lower in cyclopentane and cyclopentene than in cyclohexane and cyclohexene, due to a smaller eclipsing strain in the five-membered radicals relative to the parent molecules (six-membered hydrocarbons and their radicals are essentially strain free). (2) C-H BDEs in cyclopentene and cyclohexene leading to the allyl radicals are similar because cyclopenten-3-yl has almost as much strain as its parent molecule, due to a synperiplanar configuration. (3) The C-H BDE in 1,3-cyclopentadiene is 27 kJ mol (-1) higher than in 1,4-cyclohexadiene due to the stabilizing effect of the conjugated double bond in 1,3-cyclopentadiene and not to a destabilization of the cyclopentadienyl radical. The chemical insight afforded by group additivity methods in choosing the correct model for SE estimation is highlighted.     

Altering the allowed/forbidden gap in cyclobutene electrocyclic reactions: experimental and theoretical evaluations of the effect of planarity constraints

The allowed conrotatory cyclobutene ring-opening has a distinctly nonplanar carbon skeleton. Classic experiments by Brauman and Archie, and by Freedman et al., placed the allowed/forbidden gap at greater than 15 kcal/mol. Wolfgang Roth proposed that a system forced to planarity might have a smaller preference for the conrotatory mode than unconstrained systems. Such systems have now been studied theoretically and experimentally, and results that confirm Roth's postulate are presented here. The experiments were performed in Bochum, and the calculations were carried out in Osaka and Los Angeles. As the cyclobutene ring-opening transition structure approaches planarity, the energy gap between allowed conrotatory and the forbidden disrotatory pathways decreases. For the ring-opening of a cyclobutene fused to norbornene, the energy gap between the forbidden and the allowed transition state is only 4.1 kcal/mol by CASSCF and 8.0 kcal/mol by CAS-MP2 as compared to 13.4 and 19.2 kcal/mol, respectively, for the parent cyclobutene. Experimental studies of 3,4-dimethylcyclobutenes fused to various ring systems are reported, and a trend is found toward a reduced allowed/forbidden gap as the planarity of the cyclobutene is enforced.     

The concept of protobranching and its many paradigm shifting implications for energy evaluations

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.     

Singlet-triplet energy separation of cyclobutylidene

Ab initio (MP2, CCSD(T)) and density functional theory (BLYP, B3LYP) calculations provide insight concerning novel aspects of structure and bonding in cyclobutylidene (1). Singlet cyclobutylidene ((1)1) adopts a bicyclobutane-like structure (C(s) symmetry) that includes a weak, transannular bonding interaction between the carbene carbon and the opposing CH(2) group. Conformational ring inversion in (1)1 occurs through a transition state of C(2)(v)() symmetry (TS(1)1) with an enthalpy barrier of approximately 3 kcal/mol. Stabilization afforded the singlet state by the transannular interaction appears to be largely offset by a loss of hyperconjugative stabilization from the adjacent C-H bonds. Triplet cyclobutylidene ((3)1) exhibits a C(2)(v)() structure and conventional bonding. The triplet state lies 5.9 kcal/mol above the singlet ground state at the CCSD(T)/TZP//CCSD(T)/DZP level of theory. The singlet-triplet energy gap of cyclobutylidene (-5.9 kcal/mol) lies between that of an acyclic analogue, dimethylcarbene (-1.6 kcal/mol), and a highly strained analogue, cyclopropylidene (-13.8 kcal/mol). The magnitude of the energy gap suggests that triplet cyclobutylidene ((3)1) will be thermally accessible under a variety of experimental conditions.     

Ab initio study of the J(CC) indirect nuclear spin-spin coupling constants in cyclobutane and related systems

Non-empirical calculations using the equations-of-motion approach, which incorporates the main portion of the electron correlation effects, are reported for the carbon-carbon nuclear spin-spin coupling constants in cyclobutane, bicyclobutane, tricyclobutane, cyclobutene, cyclobutyne, cyclobutadiene, bicyclobutene, methylenecyclopropane, and methylenecyclopropene. The results provide an overall picture of the influences exerted on sign and magnitude of the J(CC) by progressive condensation, unsaturation, and branching rearrangement of the cyclobutane frame.     

Benzocyclobutene: The Impact of Fusing a Strained Ring onto Benzene

The gas-phase acidities of the two aromatic sites in benzocyclobutene were measured in a Fourier transform mass spectrometer using a kinetic technique (i.e., the DePuy method). Fusion of a cyclobutane ring onto benzene is found to have a slight acidifying effect at the alpha-position (3.2 +/- 1.7 kcal mol(-)(1)) and little, if any, influence on the beta-site (0.8 +/- 1.9 kcal mol(-)(1)). Energetic data (DeltaH degrees (acid) = 386.2 +/- 3.0 kcal mol(-)(1), EA = 0.84 +/- 0.11 eV, and C-H BDE = 92 +/- 4 kcal mol(-)(1)) for the benzylic position were obtained via the bracketing technique and application of a thermodynamic cycle. Differences in the reactivities of the three conjugate bases also were explored. Ab initio and density functional theory calculations were carried out to provide geometries, energies, and insights into the carbanions' electronic structures.     

Conformation-dependent reaction thermochemistry: study of lactones and lactone enolates in the gas phase

Gas-phase acidities (Delta H degrees (acid)) of lactones with ring sizes from four to seven have been measured on a Fourier transform ion cyclotron resonance mass spectrometer. Electron affinities (EAs) of the corresponding lactone enolate radicals were measured on a continuous-wave ion cyclotron resonance mass spectrometer, and the bond dissociation energies (BDEs) of the alpha C-H bonds were derived. In order of increasing ring size, Delta H degrees (acid) = 368.7 +/- 2., 369.4 +/- 2.2, 367.3 +/- 2.2, and 368.3 +/- 2.2 kcal/mol and BDE = 99.4 +/- 2.3, 94.8 +/- 2.3, 89.2 +/- 2.3, and 92.8 +/- 2.4 kcal/mol for beta-propiolactone, gamma-butyrolactone, delta-valerolactone, and epsilon-caprolactone, respectively. For their corresponding enolate radicals, EA = 44.1 +/- 0.3, 38.8 +/- 0.3, 35.3 +/- 0.3, and 37.9 +/- 0.6 kcal/mol. All of these lactones are considerably more acidic than methyl acetate, consistent with a dipole repulsion model. Both BDEs and EAs show a strong dependence on ring size, whereas Delta H degrees (acid) does not. These findings are discussed, taking into account differential electronic effects and differential strain between the reactant and product species in each reaction.     

A stable silicon congener of highly strained bicyclo[3.2.0]hepta-1,3,6-triene

A silicon-containing fused bicyclic compound with a highly strained bridgehead double bond, 2,3,6,7-tetra-tert-butyl-4-(tert-butyldimethylsilyl)-5-(tert-butyldimethylsiloxy)-5-silabicyclo[3.2.0]hepta-1,3,6-triene (2), was synthesized quantitatively by the reaction of 1,2-bis-tert-butyl-4,4-bis(tert-butyldimethylsilyl)-4-silatriafulvene (3) with di-tert-butylcyclopropenone (4) at 80 degrees C. An X-ray crystallographic analysis for 2 not only confirmed a bicyclic structure having a silacyclopentadiene (silole) ring fused with a silacyclobutene ring but also the remarkable deformation around the double bonds; the sum of the bond angles around the unsaturated bridgehead carbon was 333 degrees . The strain energy of a model 5-silabicyclo[3.2.0]hepta-1,3,6-triene was calculated at the MP2/6-31+G(d,p)//B3LYP/6-31+G(d) level (30.2 kcal/mol) to be comparable to that for parent bicyclo[3.2.0]hepta-1,3,6-triene (30.7 kcal/mol). Despite the high steric strain, 2 was stable enough to be kept intact for several months in the air. The high stability is ascribed to the effective steric protection of the ring system by the bulky substituents.     

Cycloalkane and cycloalkene C-H bond dissociation energies

Both C-H bond dissociation energies for cyclobutene were measured in the gas phase (BDE = 91.2 +/- 2.3 (allyl) and 112.5 +/- 2.5 (vinyl) kcal mol-1) via a thermodynamic cycle by carrying out proton affinity and electron-binding energy measurements on 1- and 3-cyclobutenyl anions. The results were compared to those for an acyclic model compound, cis-2-butene, and provide the needed information to experimentally establish the heat of formation of cyclobutadiene. Chemically accurate G3 and W1 calculations also were carried out on cycloalkanes, cycloalkenes, and selected reference compounds. It appears that commonly cited bond energies for cyclopropane, cyclobutane, and cyclohexane are 3 to 4 kcal mol-1 too small and their pi bond strengths, as given by BDE1 - BDE2, are in error by up to 8 kcal mol-1.     

CH...O and CH...F links form the cage structure of dioxane-trifluoromethane

The molecular beam Fourier transform microwave spectrum of 1,4-dioxane-trifluoromethane has been assigned and measured. The two subunits form a cage stabilized by one C-H...O and two C-H...F weak hydrogen bonds. The C-H...O link involves the axial lone pair of one of the two equivalent ring oxygens, while the two C-H...F bridges connect trifluoromethane to the two axial hydrogens in positions 3 and 5. The dissociation energy has been estimated from the D(J) centrifugal distortion parameter to be approximately 6.8 kJ/mol.     

Oxidative addition of the fluoromethane C-F bond to Pd. An ab initio benchmark and DFT validation study

We have computed a state-of-the-art benchmark potential energy surface (PES) for two reaction pathways (oxidative insertion, OxIn, and S(N)2) for oxidative addition of the fluoromethane C-F bond to the palladium atom and have used this to evaluate the performance of 26 popular density functionals, covering LDA, GGA, meta-GGA, and hybrid density functionals, for describing these reactions. The ab initio benchmark is obtained by exploring the PES using a hierarchical series of ab initio methods (HF, MP2, CCSD, CCSD(T)) in combination with a hierarchical series of seven Gaussian-type basis sets, up to g polarization. Relativistic effects are taken into account through a full four-component all-electron approach. Our best estimate of kinetic and thermodynamic parameters is -5.3 (-6.1) kcal/mol for the formation of the reactant complex, 27.8 (25.4) kcal/mol for the activation energy for oxidative insertion (OxIn) relative to the separate reactants, 37.5 (31.8) kcal/mol for the activation energy for the alternative S(N)2 pathway, and -6.4 (-7.8) kcal/mol for the reaction energy (zero-point vibrational energy-corrected values in parentheses). Our work highlights the importance of sufficient higher angular momentum polarization functions for correctly describing metal-d-electron correlation. Best overall agreement with our ab initio benchmark is obtained by functionals from all three categories, GGA, meta-GGA, and hybrid DFT, with mean absolute errors of 1.4-2.7 kcal/mol and errors in activation energies ranging from 0.3 to 2.8 kcal/mol. The B3LYP functional compares very well with a slight underestimation of the overall barrier for OxIn by -0.9 kcal/mol. For comparison, the well-known BLYP functional underestimates the overall barrier by -10.1 kcal/mol. The relative performance of these two functionals is inverted with respect to previous findings for the insertion of Pd into the C-H and C-C bonds. However, all major functionals yield correct trends and qualitative features of the PES, in particular, a clear preference for the OxIn over the alternative S(N)2 pathway.     

Oxa-bicyclocalixarenes: a new cage for anions via C-H...anion hydrogen bonds and anion...pi interactions

Density functional theory calculations indicate that the cage molecule 4 can trap F- in the gas phase (-80.5 kcal/mol) as well as in CH2Cl2 (-14.7 kcal/mol) via strong C-H...F- hydrogen bonds and pi...F- interaction.     

Kinetics of the thermal isomerization of 1,1,2‐trimethylcyclopropane

The Arrhenius parameters for the gas phase, unimolecular structural isomerizations of 1,1,2‐trimethylcyclopropane to three isomeric methylpentenes and two dimethylbutenes have been determined over a wide range of temperatures, 688–1124 K, using both static and shock tube reactors. For the overall loss of reactant, E_a = 63.7 (± 0.5) kcal/mol and log₁₀ A = 15.28 (± 0.12). These values are higher by 2.6 kcal/mol and 0.7–0.8 than previously reported from experimental work or predicted from thermochemical calculations. E_a for the formation of trans‐4‐methyl‐2‐pentene is 1.5 kcal/mol higher than E_a for the formation of the cis isomer, which is identical to the E_a difference previously reported for the formation of trans‐ and cis‐2‐butene from methylcyclopropane. Substitution of methyl groups for hydrogen atoms on the cyclopropane ring is expected to weaken the C? C ring bonds, and it has been reported previously that activation energies for structural isomerizations of methylcyclopropanes do decrease substantially over the series cyclopropane > methylcyclopropane > 1,1‐ or 1,2‐dimethylcyclopropane. However, the present study shows that the trend does not continue beyond dimethylcyclopropane isomerization. Besides reductions in C? C bond energy, steric interactions may be increasingly important in determining the energy surface and conformational restrictions near the transition state in isomerizations of the more highly substituted methylcyclopropanes. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 475–482, 2006     

A computational investigation of the reactions of methylene, chlorocarbene, and dichlorocarbene with cyclopropane

The reactions of CH(2), CHCl, and CCl(2) with cyclopropane, 1, have been examined computationally. In all cases the lowest energy reaction between the carbene and 1 is predicted to be C-H insertion. In the reaction of CH(2) with 1, the transition state for C-C insertion leading to cyclobutane is 1.7 kcal/mol higher in enthalpy than the transition state for C-H insertion at the G3B3 level. A pathway higher in energy than C-H insertion in the reactions of CHCl and CCl(2) with 1 involves two-bond cleavages generating ethylene along with chloro and dichloroethylene, respectively.