A ¹³C‐ and ¹⁵N‐NMR. Study of Some 1‐Aryl‐3, 3‐dimethyl Triazene Derivatives

Abstract

13C-and ISX-NMK. spectra have been measured for a series of triazencs. The results are compatible with the significant contribution of a structure such as 11. One-bond nitrogen-nitrogen coupling constants are reported.There is a relatively widespread distribution of molecules containing nitrogen in which this heteroatom is involved in an extended z-system. In these cases it is possible that there is a considerable delocalization of charge density from (or to) the nitrogen from other atoms in the system. Triazenes of type 1 represent one such class of molecules. For a wide variety of X-groups, a dipolar structure, such as 2, is thought [l] to be important. Indeed, variable temperature 1H-NMR. studies have already demonstrated [l] that restricted rotation exists about the N(2)-N(3) 'single' bond. While 1H-NMR. has shown that the methyl groups of 1 are not equivalent it is interesting to ask whether or not this non-equivalence stems only from 2 or whether a structure such as 3 makes a major contribution since, in both structures, alkyl groups on the amino-nitrogen would lie in magnetically non-equivalent sites. Since 3 implies a change in the nature of the carbon z-system, whereas 2 results primarily from changes at the nitrogen centers, a combined 1% and 15N-NMR. study should be valuable as both of these forms of magnetic resonance are capable of monitoring changes in charge density at the nuclear center. To further this end we have synthesized and measured the 15N-(I = 1/2, natural abundance = 0.360/) and 13C-NMR. characteristics of two series of such triazenes with one set containing 15N (greater than 95 atom yo 15N) at positions N(1) and N(2) and a second set enriched at positions N(2) and N(3).

Triazenes by Acid‐Mediated Opening of the Dihydro‐1,2,3‐triazole Ring of1,3‐Dipolar Cycloadducts of Organic Azides to Cyclic Ketene N,N‐Acetals

“…However, the observed 13 C chemical shifts for the ipso-carbon (δ =141.5 ppm) and ortho carbons (δ =114.3 ppm), are not compatible with this tautomer whose ipso-carbon and ortho-carbons are expected to resonate around 150 and 120 ppm, respectively, as in 3,3-dialkyl-1-phenyltriazenes. [20] Instead, the observed 13 C shifts closely resemble those of 3-phenyltriazenes. [21] Furthermore, the Nproton resonates at very low field (δ =12.4 ppm, in [D 6 ]dimethyl sulfoxide) as expected for tautomer 2bBF 4 (12.2-12.8 ppm) while the signal of the N-proton of tautomer 2bЈBF 4 is expected to appear at 10.9-11.6 ppm.…”

Preparation of trialkyltriazenes. A comparison of the nitrogen-nitrogen bond rotation in trialkyltriazenes and aryldialkyltriazenes by variable temperature carbon-13 NMR

“…1 -Benzyl-3-methyltriazene (3) was isolated in 95% yield: NMR (CDCI3) 1.58 (very broad band, 1 ), 3.18 (s, 3 ), 4.70 (s, 2 H), 7.34 (s, 5 H); mass spectrum m/z 149 (M+), 91 (100.00, tropylium ion). 1 -Benzyl-3-n-butyltriazene (4) was isolated in 92% yield:…”

“…Alkylation of l-Benzyl-3-n-butyltriazene (4). 4 was alkylated according to established procedures using 1.91 g (0.01 mol) with 1.35 g (0.012 mol) of potassium ZerZ-butoxide and 2.82 g (0.02 mol) of methyl iodide. Workup, followed by purification on an alumina col- urrin (eluent hexane-ether, 20:1), afforded a mixture of two positional isomers in 91% yield.…”

Comparison of the Thermal Stabilities of Diazonium Salts and Their Corresponding Triazenes

“…Our 13 C NMR data for the triazene series suggest that these molecules undergo restricted rotation, as previously reported for such materials (i.e., variable temperature 13 C NMR experiments demonstrate temperature-dependent coalescence behaviour). 27,[39][40][41][42][43][44][45][46] There is inconsistency in the manner in which this issue is reported in the literature -in some cases, the observation of fewer 13 C environments than expected is not even addressed, while other cases simply note that the NMR data are inconsistent with the proposed structure (with reference to the restricted rotation phenomenon). To address this issue more rigorously, the present paper reports 13 C NMR data at three different temperatures for each triazene studied (see Supporting Information), and we also demonstrate how these temperature-dependent 13 C NMR data can be used to calculate the rotational energy barrier in the case of triazene 8b.…”