Rotational Spectra and Structures of Phenyl Isocyanate and Phenyl Isothiocyanate

Sun, Wenhao; Silva, Weslley G. D. P.; Wijngaarden, Jennifer van

doi:10.1021/acs.jpca.8b11877

Cited by 13 publications

(15 citation statements)

References 41 publications

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“…This is consistent with the previously reported geometries of phenyl-NCO and phenyl-NCS which found no differences in the electronic structure of the ring backbone despite the possibility of a change in πdelocalization of the ring with added -NCO or -NCS substituents. 19 The terminal chalcogen atom does, however, influence the geometry around nitrogen as observed from the ~15 o increase in the C4-N-C3 bond angle upon replacing oxygen with sulfur. The increased angle around nitrogen in allyl-NCS is accompanied by a decrease in the C4-N and N-C3 re bond lengths.…”

Section: Discussionmentioning

confidence: 99%

“…Comparison of the geometries of HCCNCO 17 and HCCNCS, 18 for example, have shown that changing from oxygen to sulfur results in an increase in the CNC bond angle from 140.7º to 180º. In the phenyl (Ph) containing analogues, 19 the difference in the CNC bond angle increases by a smaller amount (~10º) from 135.2º in PhNCO to 145.1º in PhNCS which is related to a change in the hybridization at nitrogen from a ~sp 1.6 -to a ~sp-hybridized orbital in these two compounds, respectively. Exploring related pairs of compounds with different R groups will provide greater insight into the role of the R substituent and terminal chalcogen on the electronic structures of NCO/NCS-containing species.…”

Section: Introductionmentioning

confidence: 99%

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Conformers of Allyl Isothiocyanate: A Combined Microwave Spectroscopy and Computational Study

et al. 2020

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The pure rotational spectrum of allyl isothiocyanate (CH2=CHCH2-NCS) was collected from 4-26 GHz using Fourier transform microwave (FTMW) spectroscopy. Its analysis revealed the presence of two conformers that arise due to variation in the CCCN and CCNC dihedral angles.The observed spectrum is consistent with the accompanying potential energy surfaces derived using quantum chemical calculations at the B3LYP-D3(BJ) and MP2 levels of theory. Together, this experimental and theoretical study unequivocally identifies a new conformer (I) as the global minimum geometry. The spectral assignment of this new conformer is verified by the observation of transitions consistent with its 34 S, 13 C and 15 N isotopologues and with the characteristic 14 N quadrupole hyperfine patterns. For conformer I, the substitution (rs) and effective ground state (r0) structures were derived and reveal contributions from a large amplitude motion in the CCNC angle.The remaining geometric parameters compare well with the equilibrium structure (re) from B3LYP-D3(BJ)/cc-pVQZ calculations. The derived CNC bond angle of 152.6(3) o for conformer I of allyl-NCS is found to be ~15 o larger than that of allyl-NCO (137.5(4) o ), which is in line with a change in the hybridization at nitrogen from an orbital with more ~sp character in allyl-NCS to ~sp 1.5 in allyl-NCO as determined via natural bond orbital analyses.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Conformers of Allyl Isothiocyanate: A Combined Microwave Spectroscopy and Computational Study

et al. 2020

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“…This fact makes the above-mentioned mechanism plausible in the condition of excess alcohol. On the other hand, isocyanates also have potential to form associates due to its large permanent electric dipole moment (|μ tot,MP2/aug-cc-pVTZ | = 2.78 D [17], |μ tot,MW | = 2.81 D [18]). Indeed, Lenzi et al reported interaction energy of 24.3–32.8 kJ/mol for alkyl-isocyanates dimers using density functional theory (DFT) calculation [19]; therefore, these isocyanate associates can also be formed in isocyanate excess and can provide a starting point for urethane formation.…”

Section: Introductionmentioning

confidence: 99%

Urethane Formation with an Excess of Isocyanate or Alcohol: Experimental and Ab Initio Study

et al. 2019

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A kinetic and mechanistic investigation of the alcoholysis of phenyl isocyanate using 1-propanol as the alcohol was undertaken. A molecular mechanism of urethane formation in both alcohol and isocyanate excess is explored using a combination of an accurate fourth generation Gaussian thermochemistry (G4MP2) with the Solvent Model Density (SMD) implicit solvent model. These mechanisms were analyzed from an energetic point of view. According to the newly proposed two-step mechanism for isocyanate excess, allophanate is an intermediate towards urethane formation via six-centered transition state (TS) with a reaction barrier of 62.6 kJ/mol in the THF model. In the next step, synchronous 1,3-H shift between the nitrogens of allophanate and the cleavage of the C–N bond resulted in the release of the isocyanate and the formation of a urethane bond via a low-lying TS with 49.0 kJ/mol energy relative to the reactants. Arrhenius activation energies of the stoichiometric, alcohol excess and the isocyanate excess reactions were experimentally determined by means of HPLC technique. The activation energies for both the alcohol (measured in our recent work) and the isocyanate excess reactions were lower compared to that of the stoichiometric ratio, in agreement with the theoretical calculations.

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“…In recent years, there has been significant experimental research progress on substituted isocyanate molecules including substituents such as, -CN, 1 -ClSO 2 , 2 -CCH, 3,4 CH 3 , 5,6 -Ph, 7,8 -CH 2 CH 2 Cl, 9 -t-Bu, 10 and many more [11][12][13][14] Isocyanic acid (HNCO) is the lowest energy isomer of the HNCO system and the simplest isocyanate, 15,16 an important class of molecules for many diverse chemical contexts. HNCO is an atmospheric pollutant formed via the burning of fossil fuels, cigarette use, and other secondary sources.…”

Section: Introductionmentioning

confidence: 99%

“…Cl, and CN) consists of larger substituents that are more relevant to industrial applications. 3,7,8 Three important autocatalyitc mechanisms (RNCO+2 H 2 O, RNCO+3 H 2 O, and H 2 O+2 RNCO) are characterized considering a smaller subset of the aforementioned substituents. The influence of these substituents on their efficiency is systematically studied for the first time.…”

Section: Introductionmentioning

confidence: 99%

Catalyzed Reaction of Isocyanates (RNCO) with Water

Wolf¹,

Vandezande

Schaefer³

2021

Preprint

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The reactions between substituted isocyanates (RNCO) and other small molecules (e.g. water, alcohols, and amines) are of significant industrial importance, particularly for the development of novel polyurethanes and other useful polymers. We present very high level ab initio computations on the HNCO + H 2 O reaction, with results targeting the CCSDT(Q)/CBS//CCSD(T)/cc-pVQZ level of theory. Our results affirm that hydrolysis can occur across both the N− −C and C− −O bonds of HNCO via concerted mechanisms to form carbamate or imidic acid with ∆H 0K barrier heights of 38.5 and 47.5 kcal mol −1 . A total of 24 substituted RNCO + H 2 O reactions were studied.Geometries obtained with a composite method and refined with CCSD(T)/CBS single point energies determine that substituted RNCO species have a significant influence on these barrier heights, with an extreme case like fluorine lowering both barriers by close to 20 kcal mol −1 and most common alkyl substituents lowering both by approximately 4 kcal mol −1 . Natural Bond Oribtal (NBO) analysis provides evidence that the 1 predicted barrier heights are strongly associated with the occupation of the in-plane C−O* orbital of the RNCO reactant. Key autocatalytic mechanisms are considered in the presence of excess water and RNCO species. Additional waters (one or two) are predicted to lower both barriers significantly at the CCSD(T)/aug-cc-pV(T+d)Z level of theory with strongly electron withdrawing RNCO substituents also increasing these effects, similar to the uncatalyzed case. The 298 K Gibbs energies are only marginally lowered by a second catalyst water molecule, indicating that the decreasing ∆H 0K barriers are offset by loss of translational entropy with more than one catalyst water. Two-step 2 RNCO + H 2 O mechanisms are characterized for the formation of carbamate and imidic acid. The second step of these two pathways exhibits the largest barrier and presents no clear pattern with respect to substituent choice. Our results indicate that an additional RNCO molecule might catalyze imidic acid formation but have less influence on the efficiency of carbamate formation. We expect that these results lay a firm foundation for the experimental study of substituted isocyanates and their relationship to the energetic pathways of related systems.

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Rotational Spectra and Structures of Phenyl Isocyanate and Phenyl Isothiocyanate

Cited by 13 publications

References 41 publications

Conformers of Allyl Isothiocyanate: A Combined Microwave Spectroscopy and Computational Study

Conformers of Allyl Isothiocyanate: A Combined Microwave Spectroscopy and Computational Study

Urethane Formation with an Excess of Isocyanate or Alcohol: Experimental and Ab Initio Study

Catalyzed Reaction of Isocyanates (RNCO) with Water

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