Azolyl group

In ref. [178] other tri(azolyl)phosphines are used for the synthesis of uridine-, adenosine-, and cytidine-oligoribonucleotides according to this method, with azolyl groups... 

Phosphoric bis- or trisazolides can also be used for the modification of nucleobases. As mentioned before with ammonia the azolyl group is easily exchanged against the amino group. 

Scheme 3.2 shows the ligand series used in the first part of this work. In the pyrimidine, pyridazine and triazine derivatives, the azolyl groups are sufficiently... 

It is instructive to consider iV-substituted azoles in reverse, i.e. the azole ring as the substituent linked to some other group. Hammett and Taft cr-constant values for azoles as substituents are given in Table 12. The values show that all A -azolyl groups are rather weak net resonance donors, imidazolyl-1 being the strongest. They are all rather strong inductive acceptors, with pyrazole considerably weaker in this respect than imidazole or the triazoles. 

Cp deriva ti ves.163 In the sold state, the two Tp ligands of 510 bind in an asymmetric k3 fashion, such that two pyrazolyl donors are strongly bound (d(Pd—N) 2.16 A), while the third interacts weakly (d(Pd—N) 2.64 A). This was interpreted as a formal 5-coordinate geometry correlating with the presumed intermediate responsible for equilibration of all pyr-azolyl groups in the solution phase. The metal metal bond of 510 was considered to be weak, on the basis of full occupancy of the a and n orbitals of the Pd2(CNXyl)2 core. 

X = iV-azolyl groups), Frolov et al. used the Katritzky equation (70JA6861) to calculate the CTr constants for some A/-azolyl groups (80IZV1562) (Table XI). 

According to Fong the increase in the inductive effects of N-azolyl groups in the sequence shown in Fig. 2 is closely connected with the concept of group electronegativity (80AJC1763). This sequence has been observed in the... 

Fig. 2. Sequence of increase of inductive effects in N-azolyl groups.

For the series of substituted five-membered heteroaromatic groups with two and more heteroatoms in the ring the a constants are known for quite a number of substituted Af-azolyl groups and there are comparatively few data for substituted five-membered C-heteroaromatic groups with two and more heteroatoms in the ring. 

To calculate the ff, and constants for substituted N-azolyl groups, Fong used Eqs. (21) and (22) (80AJC1763). 

The NH2 chemical shifts in the PMR spectra of A-(p-aminophenyl) derivatives of azoles were used to estimate the constants for some substituted A/-azolyl groups (series 3 X = jV-azolyl groups) (74JCS(P 2)449). The constants for these groups are obtained also by alkaline hydrolysis of the corresponding phthalimide dyes (84CB2275). 

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