A colorimetric detection susceptible to the dimensions of guest counteranions has been demonstrated by using poly(phenylacetylene) with L-leucine and urea functionalities (poly-PA-Leu). Poly-PA-Leu was prepared from N-(4-ethynylphenylcarbamoyl)-L-leucine ethyl ester (PA-Leu) by using [Rh(+){eta(6)-C(6)H(5))B(-)(C(6)H(5))(3)}(2,5-norbornadiene)] as a catalyst. The biased helical conformation of poly-PA-Leu was demonstrated through Cotton effects in the circular dichroism (CD) spectra. The addition of ammonium salts, including tetra-n-butylammonium acetate, tetra-n-butylammonium chloride, and tetra-n-butylammonium bromide anions (CH(3)COO(-), Cl(-), and Br(-)), into the poly-PA-Leu solution intensified the CD responses of poly-PA-Leu, which is indicative of the chiral adjustability of anion recognition by using urea groups. In addition, the combination of poly-PA-Leu with the CH(3)COO(-), Cl(-), and Br(-) anions promoted large redshifts in the absorption spectra, thus providing dramatic color changes from pale yellow to red. Guest dependency in the CD and UV/Vis spectra was clearly correlated with the size of the counteranions. Fundamentally, the addition of tetra-n-butylammonium nitrate, tetra-n-butylammonium hydrogen sulfate, tetra-n-butylammonium perchlorate, tetra-n-butylammonium azide, tetra-n-butylammonium fluoride, and tetra-n-butylammonium iodide anions (NO(3) (-), HSO(4) (-), ClO(4) (-), N(3) (-), F(-), and I(-)) has no effect on either the CD or UV/Vis profiles of poly-PA-Leu. The guest specificity observed in the CD and UV/Vis spectra clearly demonstrated the guest-dimension selectivity of poly-PA-Leu in counteranion recognition.

Three-dimensionally organized amide groups have been demonstrated to show a high sensitivity toward anionic guests using poly(phenylacetylene)s with L-leucine and amide functionalities (poly-PA-Leu). The poly-PA-Leu was prepared from the N-(4-ethynylphenylcarbonyl)-L-leucine ethyl ester (PA-Leu) using Rh + (2,5-norbornadiene)[(η 6 -C 6 H 5 )B -(C 6 H 5 ) 3 ] (Rh(nbd)BPh 4 ) as a catalyst. The biased helical conformation of poly-PA-Leu was demonstrated through Cotton effects in the circular dichroism (CD) spectra. The addition of ammonium salts including acetate, fluoride, benzoate, azide, and bromide (CH 3 COO -, F -, C 6 H 5 COO -, N 3 -, and Br -, respectively) into the poly-PA-Leu solution intensified the CD responses of the poly-PA-Leu, indicative of the polyacetylene helicity changes triggered by anion recognition of the amide groups. The efficient anion binding was observed for poly-PA-Leu with CH 3 COO -, whose apparent binding constant was estimated to be 1.1 × 10 3 (mol -1 • L). On the other hand, the anions including perchlorate (ClO 4 -), nitrate (NO 3 -), chloride (Cl -), and iodide (I -) had essentially no effects on both the CD and UV profiles of poly-PA-Leu. The guest specificity observed in the CD spectra of poly-PA-Leu with counteranions clearly correlated with the guest-basicity.

Self-association of dipolar substances is studied by 13C magnetic resonance. The dilution shifts in carbon tetrachloride are analyzed in terms of the monomer–dimer equilibrium. Downfield 13C shifts of the nitrile and carbonyl groups are observed for the formation of the dimer of acetone, acetonitrile, and ethyl acetate. Upfield 13C shifts, on the other hand, are observed in the methyl and methylene groups of acetone, methylethyl ketone, ethyl acetate, acetonitrile, propionitrile, nitromethane, nitroethane, N,N-di-methylformamide, and N,N-dimethylacetamide. The equilibrium constants are 0.1–0.5 in units of mole fraction. The downfield 13C shifts of the nitrile and carbonyl groups are interpreted in terms of electric (reaction) field effects imposed by another molecule through dimer formation. The alternation of polarity by polarization of the X–Y group explains the upfield 13C shifts of methyl and methylene groups as shown in the following scheme: Hs+—C−—X+—Y−, where X—Y stands for C=O, C≡N, and NO2 groups which have been classified as –I− groups by Pople and Gordon.

I4N shifts of fiveand six-membered N-heterocycles have been determined by the -{ 14N} heteronuclear double resonance method with the aid of two-and three-bond N-H spin couplings. Applicability of this technique depends considerably upon properties of solvents which are responsible for an extent of the quadrupole relaxation effect. The amount of sharpening of the C-H proton peak by irradiation of 14N nuclei was observed to be 10-70%. For the determination of the 14N shift of five-membered N-heterocycles, in which coalescence of 14N signals between two kinds of nitrogen atoms (N and N-H) occurs by the rapid proton exchange, jV-methyl derivatives were also employed for comparison. By comparison of 14N shifts between a parent molecule and its TV-methyl derivative, tautomeric forms in five-membered N-heterocycles are discussed. Further 14N

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