Hindered Internal Rotation about a C-N Bond in Some Trisubstituted 1,3,5-Triazines

Abstract

We have studied the temperature dependence of the 1 H NMR spectra of some 2,4,6-trisubstituted 1,3,5-triazines having an NHAlk or NAlk 2 group or groups at the position 2 or 2 and 4 of the heterocycle. We have shown that rotation of these groups about the C-N bond is hindered. We have calculated the free energies of activation for the rotation processes.Keywords: 2,4,6-trisubstituted 1,3,5-triazines, hindered internal rotation, isomers, free energy of activation.In the 1 H NMR spectra of triazine derivatives containing NHAlk or NAlk 2 substituents at the positions 2 and 4 of the heterocycle, we observed two or more sets of signals from protons of the N-alkyl and NH groups which may be connected with the presence in the solutions of different isomeric forms of the indicated compounds [1]. In order to study this question, we recorded the 1 H NMR spectra of trisubstituted triazines 1-3 in the temperature range 20-90°C. 1 a R 1 = R 2 = NMe 2 , R 3 = Cl; b R 1 = NMe 2 , R 2 = OMe, R 3 = Cl; c R 1 = NHMe, R 2 = OMe, R 3 = Cl; d R 1 = R 2 = NHEt, R 3 = CN; e R 1 = R 2 = NHCHMe 2 , R 3 = CN; f R 1 = NHEt, R 2 = NHCMe 3 , R 3 = Cl; g R 1 = NMe 2 , R 2 = OMe, R 3 = OC 6 H 4 COOEt-p; h R 1 = NHEt, R 2 = SMe, R 3 = OC 6 H 4 COOEt-p; i R 1 = R 2 = NHCHMe 2 , R 3 = OC 6 H 4 COOMe-p; 2 a R 1 = R 2 = NMe 2 , R 3 = OH; b R 1 = NMe 2 , R 2 = OMe, R 3 = OH; c R 1 = NHEt, R 2 = OMe, R 3 = OH; d R 1 = NHEt, R 2 = OMe, R 3 = OCHMe 2 ; e R 1 = R 2 = NHEt, R 3 = OH; f R 1 = R 2 = NHEt, R 3 = OEt; g R 1 = R 2 = NHCHMe 2 , R 3 = OH; h R 1 = R 2 = NHCHMe 2 , R 3 = OMe; 3 a R 1 = R 2 = NMe 2 ; b R 1 = NMe 2 , R 2 = OMe; c R 1 = NHEt, R 2 = OMe; d R 1 = R 2 = NHEt; e R 1 = R 2 = NHCHMe 2 ; a-e R 3 = Me __________________________________________________________________________________________ Armenian Agricultural Academy, Yerevan 375009;

Glass versus Crystal: A Balancing Act between Competing Intermolecular Interactions

“…Despite the fact that the π−π stacking arrangement for the dimers in Figure 2c and d is different from the classical arylperfluoroaryl interaction, it can be noted that these H-bond interaction values are comparable to the association energy reported between benzene and hexafluorobenzene in its sandwich complex form, which is −20 kJ/mol. 47 Both types of noncovalent interactions therefore seem able to compete in the viscous state with π−π stacking promoting crystallization (by limiting conformational flexibility) and the hydrogen bonding frustrating crystallization (by promoting the formation of different conformers), which is in agreement with previous studies. 29,46 Indeed, in this family of compounds, 22 the primary factor responsible for impeding crystallization was revealed to be the presence of multiple conformers with similar energies and high interconversion barriers, and hydrogen bonding was shown to contribute as a kinetic trap by providing additional cohesion between molecules in both the viscous and vitreous states.…”

“…Both types of interactions are moderately strong and are both likely to form reversibly above T g . Moreover, both interactions are weaker than the energy barrier for the rotation of the NHR groups around the triazine ring. ,, It is therefore unlikely that the relative strengths of these two particular types of interactions account for their impact on crystallization kinetics. A more likely explanation would thus involve the shape of the aggregates and their respective ability to pack efficiently.…”

Synthesis of Novel 6-(3,5-Dimethyl-1H-Pyrazol-1-yl)Pyridazin-3(2H)-One Derivatives and their Preliminary Biological Evaluation

“…This process was discussed in detail in a previous paper. 33 To introduce the 1,3,4-oxadiazole ring into the structure, the ester (4d) was at first converted into the corresponding hydrazide (8) by reaction with hydrazine hydrate (see Safety caution on hydrazine hydrate and hydrazines in the Experimental section). The heterocyclisation of 8 with carbon disulfide and KOH in an alcohol medium led to a target product with a combination of three pharmacophore heterocyclic rings (9) (Scheme 3).…”

Glass engineering of aminotriazine-based materials with sub-ambient Tg and high kinetic stability

“…The values are also close to values measured experimentally on simple aminotriazines by variable-temperature NMR. 46 The higher activation energy for the cyclohexyl-substituted compounds implies less interconversion events between conformers and therefore contributes to increasing their Tg compared to the analog compounds with phenyl ancillary groups. Interestingly, this rotational barrier is lower with the amino headgroups (NHMe or NMe2) than with the ethyl or methoxy headgroups, likely a consequence of the headgroups' own resonance with the triazine ring.…”