Spectral evidence for generic charge → acceptor interactions in carbamates and esters

Prabhakaran, Erode N.; Tumminakatti, Shama; Vats, Kamal; Ghosh, Sudip

doi:10.1039/d0ra00313a

Cited by 4 publications

(6 citation statements)

References 53 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Schädel et al. reported carbamate rotational barriers of Δ G =15.2 kcal/mol and Δ G= 15.1 kcal/mol for the symmetric bis(2‐(2‐vinylsulfonyl)ethoxy)ethyl tert ‐butyl carbamate and the asymmetric methyl(2‐(2‐vinylsulfonyl)ethoxy)ethyl tert ‐butyl carbamate, respectively [12] . Wiest et al.…”

Section: Resultsmentioning

confidence: 99%

“…The analysis using the modified Eyring equation [35,36] resulted in the rotational energy barrier of A exp (II) = 15.93 � 0.59 kcal/mol, in close agreement with the computed estimate of A rot (VII). Rotational barriers were also determined experimentally for similar N,N-dialkyl O-alkyl carba- [12] Wiest et al showed that N-alkyl-Nphenyl alkyl carbamates may feature even lower rotational barriers such as ΔG = 12.3 kcal/mol for methyl(phenyl) tert-butyl carbamate. [9] The CN rotation of ureas R 4 R 3 NÀ COÀ NR 1 R 2 have been shown to be similar to carbamates but proceed with smaller rotational barriers than carbamates.…”

Section: Chemphyschemmentioning

confidence: 99%

“…determined the rotational barriers for a collection of alkyl substituted urea systems [7] . Far fewer carbamate systems have been studied in depth [8–13] …”

Section: Introductionmentioning

confidence: 99%

“…[7] Far fewer carbamate systems have been studied in depth. [8][9][10][11][12][13] In the context of our synthetic work on tertiary carbamates we needed to understand their dynamic stereochemistry. While developing syntheses for N-trifluoroethyl lysine and derivatives we worked with compounds I-V (Scheme 1).…”

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Rotation‐Inversion Isomerization of Tertiary Carbamates: Potential Energy Surface Analysis of Multi‐Paths Isomerization Using Boltzmann Statistics

Jameson

Glaser

2022

ChemPhysChem

View full text Add to dashboard Cite

Potential energy surface (PES) analyses at the SMD[MP2/6–311++G(d,p)] level and higher‐level energies up to MP4(fc,SDTQ) are reported for the fluorinated tertiary carbamate N‐ethyl‐N‐(2,2,2‐trifluoroethyl) methyl carbamate (VII) and its parent system N,N‐dimethyl methyl carbamate (VI). Emphasis is placed on the analysis of the rotational barrier about the CN carbamate bond and its interplay with the hybridization of the N‐lone pair (NLP). All rotational transition state (TS) structures were found by computation of 1D relaxed rotational profiles but only 2D PES scans revealed the rotation‐inversion paths in a compelling fashion. We found four unique chiral minima of VII, one pair each of E‐ and Z‐rotamers, and we determined the eight unique rotational TS structures associated with every possible E/Z‐isomerization path. It is a significant finding that all TS structures feature N‐pyramidalization whereas the minima essentially contain sp2‐hybridized nitrogen. We will show that the TS stabilities are affected by the synergetic interplay between NLP/CO2 repulsion minimization, NLP→σ*(CO) negative hyperconjugation, and two modes of intramolecular through‐space electrostatic stabilization. We demonstrate how Boltzmann statistics must be applied to determine the predicted experimental rotational barrier based on the energetics of all eight rotamerization pathways. The computed barrier for VII is in complete agreement with the experimentally measured barrier of the very similar fluorinated carbamate N‐Boc‐N‐(2,2,2‐trifluoroethyl)‐4‐aminobutan‐1‐ol II. NMR properties of VII were calculated with a variety of density functional/basis set combinations and Boltzmann averaging over the E‐ and Z‐rotamers at our best theoretical level results in good agreement with experimental chemical shifts δ(13C) and J(13C,19F) coupling constants of II (within 6 %).

show abstract

Section: Resultsmentioning

confidence: 99%

Section: Chemphyschemmentioning

confidence: 99%

“…determined the rotational barriers for a collection of alkyl substituted urea systems [7] . Far fewer carbamate systems have been studied in depth [8–13] …”

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Rotation‐Inversion Isomerization of Tertiary Carbamates: Potential Energy Surface Analysis of Multi‐Paths Isomerization Using Boltzmann Statistics

Jameson

Glaser

2022

ChemPhysChem

View full text Add to dashboard Cite

show abstract

“…Such compaction between H α s is characteristic of residue pairs interacting between strands in antiparallel β‐sheets [31,32] . This

H \binom{α}{A}

⋅⋅⋅

H \binom{α}{G}

ROE crosspeak intensity is only slightly reduced (43 %) in presence of a weaker H‐bond acceptor carbonyl (of Boc carbamate) [33] in 2 (Figures 3 and S4). The ROE (33 %) is retained in the N‐methylated model 3 (Figures 3 and S5) in which the alternate 12‐membered H‐bonded ring structure is not possible (Figure 3).…”

Section: Figurementioning

confidence: 97%

Hydrogen Bond Surrogate‐Constrained Dynamic Antiparallel β‐Sheets

et al. 2021

Self Cite

View full text Add to dashboard Cite

Antiparallel β‐sheets are important secondary structures within proteins that equilibrate with random‐coil states; however, little is known about the exact dynamics of this process. Here, the first dynamic β‐sheet models that mimic this equilibrium have been designed by using an H‐bond surrogate that introduces constraint and torque into a tertiary amide bond. 2D NMR data sufficiently reveal the structure, kinetics, and thermodynamics of the folding process, thereby leading the way to similar analysis in isolated biologically relevant β‐sheets.

show abstract

VT‐NMR Analysis of Rotation‐Inversion of N‐(4‐hydroxybutyl)‐N‐(2,2,2‐trifluoroethyl) tert‐butyl Carbamate: Utilizing the −CH₂CF₃ Appendage as a Reporter on E/Z‐Isomerization

Jameson,

Glaser

2024

ChemistrySelect

View full text Add to dashboard Cite

The rotational barrier about the CN carbamate bond of N‐(4‐hydroxybutyl)‐N‐(2,2,2‐trifluoroethyl) tert‐butyl carbamate 1 was determined by variable temperature (VT) 13C and 19F NMR spectroscopy. The −CH2CF3 appendage reports on rotational isomerism and allows for the observation of separate signals for the E‐ and Z‐ensembles at low temperature. The activation barrier for E/Z‐isomerization was quantified using Eyring‐Polanyi theory which requires the measurements of the maximum difference in Larmor frequency Δνmax and the convergence temperature Tc. Both Δνmax and Tc were interpolated by analyzing sigmoidal functions fitted to data describing signal separation and the quality of the superposition of the E‐ and Z‐signals, respectively. Methods for generating the quality‐of‐fit parameters for Lorentzian line shape analysis are discussed. Our best experimental value for the rotational barrier ΔGc≠(1)=15.65±0.13 kcal/mol is compared to results of a higher level ab initio study of the model N‐ethyl‐N‐(2,2,2‐trifluoroethyl) methyl carbamate.

show abstract

Spectral evidence for generic charge → acceptor interactions in carbamates and esters

Abstract: NMR, FT-IR spectral correlations of the R–O–CO groups in carbamates and esters of homologous alcohols (R) reveal R-group-dependent negative charge stabilization at the carbonyl oxygen and its donation to generic acceptors at Cα of even alkyl R.

Cited by 4 publications

References 53 publications

Rotation‐Inversion Isomerization of Tertiary Carbamates: Potential Energy Surface Analysis of Multi‐Paths Isomerization Using Boltzmann Statistics

Rotation‐Inversion Isomerization of Tertiary Carbamates: Potential Energy Surface Analysis of Multi‐Paths Isomerization Using Boltzmann Statistics

Hydrogen Bond Surrogate‐Constrained Dynamic Antiparallel β‐Sheets

VT‐NMR Analysis of Rotation‐Inversion of N‐(4‐hydroxybutyl)‐N‐(2,2,2‐trifluoroethyl) tert‐butyl Carbamate: Utilizing the −CH₂CF₃ Appendage as a Reporter on E/Z‐Isomerization

Contact Info

Product

Resources

About

Spectral evidence for generic charge → acceptor interactions in carbamates and esters

Abstract: NMR, FT-IR spectral correlations of the R–O–CO groups in carbamates and esters of homologous alcohols (R) reveal R-group-dependent negative charge stabilization at the carbonyl oxygen and its donation to generic acceptors at Cα of even alkyl R.

Cited by 4 publications

References 53 publications

Rotation‐Inversion Isomerization of Tertiary Carbamates: Potential Energy Surface Analysis of Multi‐Paths Isomerization Using Boltzmann Statistics

Rotation‐Inversion Isomerization of Tertiary Carbamates: Potential Energy Surface Analysis of Multi‐Paths Isomerization Using Boltzmann Statistics

Hydrogen Bond Surrogate‐Constrained Dynamic Antiparallel β‐Sheets

VT‐NMR Analysis of Rotation‐Inversion of N‐(4‐hydroxybutyl)‐N‐(2,2,2‐trifluoroethyl) tert‐butyl Carbamate: Utilizing the −CH2CF3 Appendage as a Reporter on E/Z‐Isomerization

Contact Info

Product

Resources

About

VT‐NMR Analysis of Rotation‐Inversion of N‐(4‐hydroxybutyl)‐N‐(2,2,2‐trifluoroethyl) tert‐butyl Carbamate: Utilizing the −CH₂CF₃ Appendage as a Reporter on E/Z‐Isomerization