Rotational barriers in five related amides

Weaver-Guevara, Holly M.; Fitzgerald, Ryan W.; Greenberg, Arthur

doi:10.1139/cjc-2016-0344

Cited by 1 publication

(5 citation statements)

References 17 publications

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“…All values of the Gibbs free energy were in the same range of 61.4 to 66.2 kJ/mol and in agreement with previously published values for carbamates . The obtained Gibbs free energies for the rotational barriers of all studied carbamates are approximately 10 kJ/mol smaller than the barriers for structurally similar acetamides …”

Section: Resultssupporting

confidence: 91%

“…In a previous study, Greenberg compared five structurally related amides with or without the ability for intramolecular hydrogen bonding. By DNMR studies and the coalescence method, it was found that hydrogen bonding contributed only little to the barriers.…”

Section: Resultsmentioning

confidence: 99%

“…These trends are in agreement with previous work on structurally related amides by Greenberg. [50] Computational calculations provided asymmetric double maximum potential energy curves for all studied carbamates, reflecting the two different transition states TS 1 and TS 2. However, the calculated trend of the ΔG ‡ values 9-OH < 3-VS < 3-OH deviated from the experimental results.…”

Section: Discussionmentioning

confidence: 98%

“…These observations suggested that steric rather than electronic factors (eg, hydrogen bonding) determine the size of the rotational barriers for the studied carbamates, ie, carbamates with smaller substituents have somewhat lower barriers than carbamates with larger substituents. These trends are in agreement with previous work on structurally related amides by Greenberg …”

Section: Discussionmentioning

confidence: 99%

“…[13,21,49] The obtained Gibbs free energies for the rotational barriers of all studied carbamates are approximately 10 kJ/mol smaller than the barriers for structurally similar acetamides. [50] The asymmetric carbamates 9-OH and 9-VS were also studied via DNMR. The rotational barriers calculated from selected NMR signals are given in Table 2, the full data set can be found in Table S2.…”

Section: Dnmr Studies Of the Carbamate-protected Aminesmentioning

confidence: 99%

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Rotational barriers of carbamate‐protected amine crosslinkers for hydrogels: A combined experimental and computational study

Schädel

Gebhardt

Löffler

et al. 2019

J of Physical Organic Chem

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Diethylenetriamines and diethanolamines carrying a carbamate‐protected amine and peripheral reactive units are valuable synthetic building blocks for hydrogel crosslinkers or biohybrid materials because they enable orthogonal functionalization. However, the carbamate unit leads to restricted rotational mobility, affecting both physical and chemical properties of the amines. To gain insight into the rotational behavior of such systems, a series of carbamate‐protected amines with different peripheral units was synthesized and their rotational barriers were studied by dynamic NMR measurements and electronic structure calculations. Experimentally observed barriers were in the range of 61 to 66 kJ/mol and were mostly dependent on the size of the peripheral groups rather than their hydrogen bonding ability. Density functional theory (DFT) and MP2 calculations yielded barriers of similar order of magnitude, albeit differing in the overall trends. The data suggest that for improved theoretical estimates of free energy barriers ab initio molecular dynamics simulations in explicit solvent would be required.

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Section: Resultssupporting

confidence: 91%

Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 98%

Section: Discussionmentioning

confidence: 99%