Two Three‐Dimensional Metal‐Organic Frameworks Constructed from Alkaline Earth Metal Cations (Sr and Ba) and 5‐Nitroisophthalicacid – Synthesis,Charaterization, and Thermochemistry

Two MOFs of [Sr^II(5‐NO₂‐BDC)(H₂O)₆] ( 1 ) and [Ba^II(5‐NO₂‐BDC)(H₂O)₆] ( 2 ) have been synthesized in water using alkaline earth metal salts and the rigid organic ligand 5‐NO₂‐H₂BDC. The compounds were characterized by elemental analysis, infrared spectrum, thermal analysis, and X‐ray crystallography. Crystal structure analyses have shown that the two complexes are isostructural as evidenced by IR spectra and TG‐DTA. Both compounds present three‐dimensional frameworks built up from infinite chains of edge‐sharing twelve‐membered rings through O–H···O hydrogen bonds. The specific heat capacities of the title complexes have been determined by an improved RD496‐III microcalorimeter with the values of (109.29 ± 0.693) J mol⁻¹ K⁻¹ and (81.162 ± 0.858) J mol⁻¹ K⁻¹ at 298.15 K, and the molar enthalpy changes of the formation reactions of complexes at 298.15 K were calculated as (4.897 ± 0.008) kJ mol⁻¹ and (2.617 ± 0.009) kJ mol⁻¹, respectively.     

A calorimetric contribution to the study of polymorphism in tetramethylammonium chloride

The heat capacity of tetramethylammonium chloride has been measured from 115 to 498 K, both for the thermodynamically stable modifications and for the form II, which is metastable below 407 K. The entropy gains at the IV → III λ-transition and at the III → II first-order transition are estimated to be 1.19 J K⁻¹ mol⁻¹ and 4.16 J K⁻¹ mol⁻¹, respectively. At 125 K, the entropy of the metastable phase II exceeds that of the stable modification IV by only 1.76 J K⁻¹ mol⁻¹. If, as has been suggested, each cation in phase II has two possible orientations, it would seem that at 125 K this disorder in phase II is largely, if not wholly, suppressed, without the appearance of any transition or thermal anomaly.Results are also recorded of test measurements of the heat capacity of the NBS sample of synthetic sapphire (α-Al₂O₃) from 138 to 515 K.     

Exploring Oxidative NHC-Catalysis as Organocatalytic Polymerization Strategy towards Polyamide Oligomers

The polycondensation of diamines and dialdehydes promoted by an N-heterocyclic carbene (NHC) catalyst in the presence of a quinone oxidant and hexafluoro-2-propanol (HFIP) is herein presented for the synthesis of oligomeric polyamides (PAs), which are obtained with a number-average molecular weight (M_n) in the range of 1.7–3.6 kg mol⁻¹ as determined by NMR analysis. In particular, the utilization of furanic dialdehyde monomers (2,5-diformylfuran, DFF; 5,5’-[oxybis(methylene)]bis[2-furaldehyde], OBFA) to access known and previously unreported biobased PAs is illustrated. The synthesis of higher molecular weight PAs (poly(decamethylene terephthalamide, PA10T, M_n = 62.8 kg mol⁻¹; poly(decamethylene 2,5-furandicarboxylamide, PA10F, M_n = 6.5 kg mol⁻¹) by a two-step polycondensation approach is also described. The thermal properties (TGA and DSC analyses) of the synthesized PAs are reported.     

Far-infrared spectra and barriers to internal rotation of ethyl nitrate

The far-infrared spectra of gaseous and solid ethyl nitrate, CH₃CH₂ONO₂, have been recorded from 500 to 50 cm⁻¹. The fundamental asymmetric torsion of the trans conformer which has a heavy atom plane has been observed at 112.50 cm⁻¹ with two excited states failing to lower frequencies, and the corresponding fundamental torsion of the gauche conformer was observed at 109.62 cm⁻¹ with two excited states also falling to lower frequencies. The results of a variable temperature Raman study indicate that the trans conformer is more stable than the gauche conformer by 328 ± 96 cm⁻¹ (938 ± 275 cal mol⁻¹). An asymmetric potential function governing the internal rotation about the CH₂O bond is reported which gives a trans to gauche barrier of 894 ± 15 cm⁻¹ (2.56 ± 0.04 kcal mol⁻¹) and a gauche to gauche barrier of 3063 ± 68 cm⁻¹ (8.76 ± 0.20 kcal mol⁻¹) with the trans conformer more stable by 220 ± 148 cm⁻¹ (0.63 ± 0.42 kcal mol⁻¹). Transitions arising from the symmetric CH₃ and NO₂ torsions are observed for both conformers, from which the threefold and twofold periodic barriers to internal rotation have been calculated. For the trans conformer the values are 1002 cm⁻¹ (2.87 kcal mol⁻¹) and 2355 ± 145 cm⁻¹ (6.73 ± 0.42 kcal mol⁻¹) and for the gauche conformer they are 981 cm⁻¹ (2.81 kcal mol⁻¹) and 2736 ± 632 cm⁻¹ (7.82 ± 1.81 kcal mol⁻¹) for the CH₃ and NO₂ rotors, respectively. These results are compared to the corresponding quantities for some similar molecules.     

Low temperature specific heats and magnetic properties of LaRh2Si2 and HoRh2Si2

Specific heats, static magnetizations and a.c. susceptibilities have been measured on polycrystalline LaRh₂Si₂ and HoRh₂Si₂. Both compounds have been confirmed to have the ThCr₂Si₂-type crystal structure down to 4 K.LaRh₂Si₂ is not superconducting and shows no ordered magnetism above 1.3 K. It has a Debye temperature θ_D = 330 K, electronic specific heat coefficient γ = 6.4mJ mol⁻¹ K⁻², temperature-independent magnetic susceptibility χ_m = 1.6 × 10⁻⁴ e.m.u. mol⁻¹, and is considered to be an ordinary metal.HoRh₂Si₂ has two peaks in the specific heat vs. temperature curve, a broad peak at 11 K and a very sharp one at 27 K. The magnetization vs. temperature curve also shows two peaks at 10 K and 29 K. The magnetic part of the specific heat obtained by subtraction of the specific heat of LaRh₂Si₂ from that of HoRh₂Si₂, provides the total entropy ΔS = 24 J mol⁻¹ K⁻¹, which is close to Rln(2J + 1) for J = 8. This fact suggests that all the excess entropy is attributed to the ground state multiplet of Ho³⁺ ion (⁵I₈) and that the lower temperature peak observed in the specific heat (and also in the magnetization) does not originate in itinerant electrons nor in an impurity phase.     

Analysis of torsional spectra of molecules with two internal C3ν, rotors—XXVI. A far infrared study of 1,1-dimethylhydrazine

The infrared spectra of 1,1-dimethylhydrazine, (CH₃)₂NNH₂, and two isotopomers, (CD₃)₂NNH₂ and (CH₃)₂NND₂, have been recorded in the region between 600 and 100 cm⁻¹. Very rich and complex spectra were obtained and analysis of the data has been carried out. The interpretation of the spectra arising from the two methyl torsional modes of the −d₀ compound was carried out using a semi-rigid model, and the resulting potential function obtained is V₃₀ = 1685 ± 12 cm⁻¹ (4.82 ± 0.04 kcal mol⁻¹); V₀₃ = 1827 ± 16 cm⁻¹ (5.22 ± 0.05 kcal mol⁻¹); V₆₀ = −92±5cm⁻¹ (−0.26 ± 0.02 kcal mol⁻¹); V₀₆ = −41 ± 6cm⁻¹ (−0.12 ± 0.02 kcal mol⁻¹) and V^′₃₃ = −51 ± 5 cm⁻¹ (−0.15 ± 0.01 kcal mol⁻¹). Ab initio gradient calculations were carried out employing the 3–21G and 6–31G* basis sets, as well as the 6–31G* basis set with electron correlation at the MP2 level. The structural parameters, conformational stability, and three-fold barriers to internal rotation have been determined and the gauche conformer is calculated to be more stable than the trans form by 783 cm⁻¹ (2.24 kcal mol⁻¹) with the MP2/6–31G* basis set. These calculations were also used to re-evaluate the previously reported assignment of the fundamental modes, and to obtain a potential function for the asymmetric torsion. All of these results are discussed and compared with corresponding quantities for some similar compounds.     

Theoretical calculation of nitro-1-(2,4,6-trinitrophenyl)-1H-azoles energetic compounds

In order to study the properties of new energetic compounds formed by introducing nitroazoles into 2,4,6-trinitrobezene, the density, heat of formation and detonation properties of 36 nitro-1-(2,4,6-trinitrobenzene)-1H-azoles energetic compounds are studied by density functional theory, and their stability and melting point are predicted. The results show that most of target compounds have good detonation properties and stability. And it is found that nitro-1-(2,4,6-Trinitrophenyl)-1H-pyrrole compounds and nitro-1-(2,4,6-trinitrop-enyl)-1H-Imidazole compounds have good thermal stability, and their weakest bond is C NO₂ bond, the bond dissociation energy of the weakest bond is 222–238 kJ mol⁻¹ and close to 2,4,6-trinitrotoluene (235 kJ mol⁻¹). The weakest bond of the other compounds may be the C NO₂ bond or the N N bond, and the strength of the N N bond is related to the nitro group on azole ring.     

Exploring the Mechanism of a Chiral N-Alkyl Imine-Based Light-Driven Molecular Rotary Motor at MS-CASPT2//CASSCF and MS-CASPT2//(TD) DFT Levels

The working mechanism including the photoisomerization and thermal isomerization steps of a chiral N-alkyl imine-based motor synthesized by Lehn et al. are revealed by MS-CASPT2//CASSCF and MS-CASPT2//(TD-)DFT methods. For the photoisomerization process of the imine-based motor, it involves both the bright (π,π*) state and the dark (n,π*) state. In addition, the MECI has similar geometry and energy to the minimum of the S₁ state, which shows that the process is barrierless and keeps the unidirectionality of rotation well; the result confirms the imine-based motor is a good candidate for a light-driven molecular rotary motor. For the thermal isomerization process of the imine-based motor, there are two even isomerization paths: one with the mechanism of the in-plane N inversion, the energy barriers of which are 29.6 kcal mol⁻¹ at MS3-CASPT2//CAM-B3LYP level and 29.2 kcal mol⁻¹ at MS3-CASPT2//CASSCF level; the other with the mechanism of ring inversion of the cycloheptatriene moiety, with energy barriers of 28.1 kcal mol⁻¹ at MS3-CASPT2//CAM-B3LYP level and 18.1 kcal mol⁻¹ at MS3-CASPT2//CASSCF level. According to the structural feature of the stator moiety, the imine molecule can be used as a two-step or a four-step light-driven rotary motor.     

Magnetische Suszeptibilität von Calcium,Strontium und Barium zwischen 295 und 3 K

The magnetic susceptibilities of calcium, strontium and barium (purified by fractional sublimation, purity at least 99.9%) have been determined in the temperature range 295-3 K. The samples are free from ferro- and paramagnetic impurities. The data of calcium are temperature independent between 295 and 45 K at 58(2) × 10⁻⁶ cm³ mol⁻¹ and then increase to 63(2) × 10⁻⁶ cm³ mol⁻¹ at 3.3 K. The susceptibility of strontium increases almost linearly from 98(2) × 10⁻⁶ to 136(2) × 10⁻⁶ cm³ mol⁻¹ in the temperature range 295-3.3 K. The data in the case of barium decrease linearly between 295 and 60 K from 31.0(5)× 10⁻⁶ to 25.5(5) × 10⁻⁶ cm³ mol⁻¹ before remaining constant down to 3 K.     

Computational and dynamic NMR investigation of 2,2-dimesityl-1,1,1,3,3,3-hexamethyltrisilane

The structure and rotational barrier for the mesityl-silicon bond of 2,2-dimesityl-1,1,1,3,3,3-hexamethyltrisilane have been investigated by ¹H- and ¹³C-variable temperature nuclear magnetic resonance (NMR) as well as by density functional theory structural calculations. The calculations show that the lowest energy structure has C₂ symmetry with nonequivalent ortho methyl groups, consistent with the crystal structure and solution NMR. The nonequivalent ortho methyl groups exchange through a C_s transition state with a calculated relative free energy of 11.0 kcal mol⁻¹. The barrier for this rotation found by dynamic NMR is 13.4 ± 0.2 kcal mol⁻¹ at 298 K.     

Solid state mechanism of the thermal dehydration of [Rh(NH3)5(H2O)]X3 (X = Cl−, Br−, I−)

The solid phase thermal deaquation-anation of [Rh(NH₃)₅(H₂O)]X₃ (X = Cl⁻, Br⁻, I⁻) has been investigated by means of isothermal TG measurements applying all the principal g(α) expressions (0.8 ⩾ α ⩾ 0.2). The values found for the activation energy are low: ≈ 95 kJ mol⁻¹ for the Cl⁻ compound; ~105 kJ mol⁻ for the Br⁻ compound and ≈110 kJ mol⁻¹ for the I⁻ compound. These data permit the assignment of the deaquation-anation mechanism of the S_N1 dissociative type, involving a square-based pyramid activated complex and elimination of water as Frenkel defects. These values are similar to those reported for the Co(III) and Ir(III) analogues, indicating that the D_q parameter is not the principal contribution to the activation energy of the dehydration-anation process.     

Polymer Photovoltaic Cells Based on Polymethacrylate Bearing Semiconducting Side Chains

Polymethacrylate with semiconducting side chains ( P1 ), synthesized by free radical polymerization, was used as a donor material for polymer solar cells. P1 is of high molecular weight (M _n = 82 kg mol⁻¹), good thermal stability, narrow band gap (1.87 eV), and low‐lying HOMO energy level (−5.24 eV). P1 possesses not only the good film‐forming ability of polymers but also the high purity of small organic molecules. Power conversion efficiencies (PCEs) of 0.63% and 1.22% have been obtained for solar cells with M1 :PC₇₁BM and P1 :PC₇₁BM as the active layers, respectively. With PC₆₁BM as the acceptor, PCEs of M1 and P1 based devices decrease to 0.61% and 0.76%, respectively. To the best of our knowledge, this is the first report that free radical polymerization can be used to prepare polymer donors for photovoltaic applications.     

Synthesis and Characterization of New Phosphorus Containing Sulfonated Polytriazoles for Proton Exchange Membrane Application

Sulfonated polytriazoles have drawn a great attention as high performance polymers and their good film forming ability. In the present study, a phosphorus containing new diazide monomer namely, bis-[4-(4′-aminophenoxy)phenyl]phenylphosphine was synthesized and accordingly, a series of phosphorus containing sulfonated polytriazoles (PTPBSH-XX) was synthesized by reacting equimolar amount of this diazide monomer (PAZ) in combination with another sulfonated diazide monomer (DSAZ) and a terminal bis-alkyne (BPALK) by the Cu (I) catalyzed azide–alkyne click polymerization. The polymers were characterized by nuclear magnetic resonance (¹H, ¹³C, ³¹P NMR) and Fourier transform infrared spectroscopic techniques. The sulfonic acid content of the copolymers also determined from the different integral values obtained from the ¹H NMR signals. The small-angle X-ray scattering results unfolded the well-separated dispersion of the hydrophilic and hydrophobic domains of the polymers. As a whole, the copolymer membranes displayed sufficient thermal, mechanical, and oxidative stabilities high with high proton conductivity and low water uptake that are essential for proton exchange membrane applications. The copolymers exhibited oxidative stability in the range of 15–24 h and had proton conductivity values were found as high as 38–110 mS cm⁻¹ at 80 °C in completely hydrated condition. Among the all copolytriazoles, PTPBSH-90 (BPALK:DSAZ:PAZ = 100:90:10) having IEC_W = 2.44 mequiv g⁻¹, showed proton conductivity as high as 119 mS cm⁻¹ at 90 °C with an activation energy of 10.40 kJ mol⁻¹ for the proton conduction. © 2020 Wiley Periodicals, Inc. J. Polym. Sci. 2020 , 58, 263–279     

Synthesis and Characterization of a Novel Poly(aryl ether) Containing 4-Chloro-2,5-diphenyloxazole

4-Chloro-2,5-bis(4-fluorophenyl)oxazole monomer has successfully been synthesized using cyclization reaction of 4-fluorobenzoyl cyanide with 4-fluorobenzaldehyde. This monomer was converted to poly(aryl ether)s by nucleophilic substitution of the fluorine atoms on the benzene rings of oxazole monomer with bisphenol A. The influence of the reaction time on the molecular weight had been investigated. The polymers were identified by FT-IR,¹H-NMR and TGA. The products exhibited weight-average molar masses up to 2.81 x 10⁴g mol⁻¹ in GPC. These poly(aryl ether)s showed very high thermal stability up to 363 °C for 5 % weight loss in TGA under N₂.     

Protonation of CO2, COS,CS2: Proton affinities and the structures of the protonated species

The geometric structures of a number of isomers of the ions formed by protonation of CO₂, COS and CS₂, and of the parent molecules themselves, have been fully optimized using ab initio quantum chemical methods. Stable minima have been found both for molecules protonated at the terminal atom and at the central carbon atom; ions of the latter type show strong near-degeneracy effects which have been ignored in previous calculations. Proton affinities of CO₂, COS and CS₂ have been calculated: for CO₂ the theoretical result (565 kJ mol⁻¹) is in excellent agreement with experiment (540 kJ mol⁻¹), given that the experimental proton affinity includes a contribution from zero-point vibration of ≈ −27 kJ mol⁻¹. For COS, for which no experimental value is available, the calculations give almost identical results for both O and S protonated species (619 and 636 kJ mol⁻¹, respectively). It may not therefore be possible to distinguish these two isomers experimentally. The theoretical result for CS₂ (678 kJ mol⁻) suggests that the current experimental value of the proton affinity (699 kJ mol⁻¹) is too high, since this value includes a zero-point vibration contribution of some −19 kJ mol⁻¹).     

Thermochemical properties from ab initio calculations: π- and σ-Free radicals of importance in soot formation: •C3H3 (propargyl), •C4H3, •C13H9 (phenalenyl), •C6H5 (phenyl), •C10H7 (naphthyl), •C14H9 (anthryl), •C14H9 (phenanthryl), •C16H9 (pyrenyl), •C12H7 (acenaphthyl), and •C12H9 (biphenylyl)

The calculated difference in the standard heat of formation Δ Δ_fH°(298.15) of n- and i-C₄H₃^• free radicals is 37.9 kJ mol⁻¹ for G3MP2B3 and 45.0 kJ mol⁻¹ for CCSD(T)-CBS (W1U) calculations, which seems to preclude the direct even-carbon radical pathway to benzene and higher PAH (polycyclic aromatic hydrocarbon) formation including soot in a hydrocarbon flame. For the phenyl-type σ-radicals listed in the title, absolute values of Δ_fH°(298.15) have been calculated using G3MP2B3-computed values of bond dissociation energies D°(298.15) and combined with experimental values of Δ_fH° (298.15) for the parent hydrocarbon because of a slight systematic overprediction of the thermodynamic stability of large PAHs by the applied computational G3MP2B3 method. Standard enthalpies of formation Δ_fH°(298.15) as well as absolute entropies S° and heat capacities C°_p are given for a series of π- and σ-free radicals important to combustion as a function of temperature. A spread of roughly 40 kJ mol⁻¹ in the average C H bond strength of PAH leading to σ-radicals has been calculated, the lowest leading to 4-phenanthryl (463.6 kJ mol⁻¹), the highest leading to 2-biphenylyl radical (502.5 kJ mol⁻¹). © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 395–415, 2008     

Effects of Chain Ends on Thermal and Mechanical Properties and Recyclability of Poly(γ-butyrolactone)

This work investigates effects of poly(γ-butyrolactone) (PγBL) with different initiation and termination chain ends on five types of materials properties, including thermal stability, thermal transitions, thermal recyclability, hydrolytic degradation, and dynamic mechanical behavior. Four different chain-end-capped polymers with similar molecular weights, BnO-[C(=O)(CH₂)₃O]_n-R, R = C(=O)Me, C(=O)CH=CH₂, C(=O)Ph, and SiMe₂CMe₃, along with a series of uncapped polymers R′O-[C(=O)(CH₂)₃O]_n-H (R′ = Bn, Ph₂CHCH₂) with M_n ranging from low (4.95 kg mol⁻¹) to high (83.2 kg mol⁻¹), have been synthesized. The termination chain end R showed a large effect on polymer decomposition temperature and hydrolytic degradation, relative to H. Overall, for those properties sensitive to the chain ends, chain-end capping renders R-protected linear PγBL behaving much like cyclic PγBL. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2271–2279     

Theoretical and experimental studies of the diketene system: Product branching decomposition rate constants and energetics of isomers

The kinetics and mechanism for the thermal decomposition of diketene have been studied in the temperature range 510–603 K using highly diluted mixtures with Ar as a diluent. The concentrations of diketene, ketene, and CO₂ were measured by FTIR spectrometry using calibrated standard mixtures. Two reaction channels were identified. The rate constants for the formation of ketene (k₁) and CO₂ (k₂) have been determined and compared with the values predicted by the Rice–Ramsperger–Kassel–Marcus (RRKM) theory for the branching reaction. The first-order rate constants, k₁ (s⁻¹) = 10^{15.74 ± 0.72} exp(−49.29 (kcal mol⁻¹) (±1.84)/RT) and k₂ (s⁻¹) = 10^{14.65 ± 0.87} exp(−49.01 (kcal mol⁻¹) (±2.22)/RT); the bulk of experimental data agree well with predicted results. The heats of formation of ketene, diketene, cyclobuta-1,3-dione, and cyclobuta-1,2-dione at 298 K computed from the G2M scheme are −11.1, −45.3, −43.6, and −40.3 kcal mol⁻¹, respectively. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 580–590, 2007     

Nickel complexes bearing different electron groups on substituted salicylaldnaphthylmethyleneimine ligands: Syntheses and their catalytic performance for (co)polymerization of norbornene

Novel nickel complexes bearing different electron groups on substituted salicylaldnaphthylmethyleneimine ligands, bis-(salicylaldnaphthylmethyleneimino)Ni(II) (Ni{(3-R¹)(5-R²)C₆H₂(O)CH[N (naphthyl-CH₂)]}₂ Ni1 : R¹ = H, R² = H; Ni2 : R¹ = H, R² = CH₃; Ni3 : R¹ = H, R² = Br; Ni4 : R¹ = H, R² = OCH₃; Ni5 : R¹ = CH₃, R² = H; Ni6 : R¹ = Br, R² = H), were synthesized. Ni2 , Ni3 , Ni5 , and Ni6 are clearly characterized by single-crystal X-ray diffraction. Co-polymerization of norbornene (NB) with 5-norbornene-2-methylene butyl ether (BN) was carried out in toluene with the aforesaid complexes as catalyst precursors and B(C₆F₅)₃ as the co-catalyst. Catalyst activity, molecular weight, thermal stability, solubility, regularity, and optical transparency were investigated, and the mechanism of the electron groups changing catalyst performance is explained. All catalysts show high activity toward co-polymerization (up to 3.53 × 10⁵ g_polymer mol_Ni⁻¹ h⁻¹). Ni3 shows the highest activity and Ni5 shows the highest insertion rate (up to 37.6%). The obtained poly(NB-co-BN)s are confirmed to be vinyl-addition-type co-polymers, and they are noncrystalline. The co-polymers exhibited excellent thermal stability and processability (T_d ≥ 400 °C, T_g < 240 °C), optical transparency (up to 90%), and good solubility.     

Far-IR spectrum,conformation stability,barriers to internal rotation,vibrational assignment,and ab initio calculations of 3-chloro-2-methylpropene

The far-IR spectrum from 375 to 30 cm⁻¹ of gaseous 3-chloro-2-methylpropene, CH₂=C(CH₃)CH₂Cl, has been recorded at a resolution of 0.10 cm⁻¹. The fundamental asymmetric torsional mode for the gauche conformer is observed at 84.3 cm⁻¹ with three excited states falling to lower frequency. For the higher energy s-cis conformer, where the chlorine atom eclipses the double bond, the asymmetric torsion is observed at 81.3 cm⁻¹ with two excited states falling to lower frequency. Utilizing the s-cis and gauche torsional frequencies, the gauche dihedral angle and the enthalpy difference between conformers, the potential function governing the interconversion of the rotamers has been calculated. The determined potential function coefficients are (in reciprocal centimeters): V₁=189±12, V₂=−358±11, V₃=886±2 and V₄=−12±2 with an enthalpy difference between the more stable gauche and s-cis conformers of 150 ±25 cm⁻¹ (430 ± 71 cal mol⁻¹). This function gives values of 661 cm⁻¹ (1.89 kcal mol⁻¹), 1226 cm⁻¹ (3.51 kcal mol⁻¹) and 812 cm⁻¹ (2.32 kcal mol⁻¹), for the s-cis to gauche, gauche to gauche, and gauche to s-cis barriers, respectively. From the methyl torsional frequency of 170 cm⁻¹ for the gauche conformer, the threefold barrier of 678 cm⁻¹ (1.94 kcal mol⁻¹) has been calculated. The asymmetric potential function, conformational energy difference and optimized geometries of both conformers have also been obtained from ab initio calculations with both the 3–21G^* and 6–31G^* basis sets. A normal-coordinate analysis has also been performed with a force field determined from the 3–21G^* basis set. These data are compared with the corresponding data for some similar molecules.