Substitutent effects of phosphorus- and arsenic-containing groups in aromatic substitution. Part 7. Comparison of carboxy and phosphonic groups

Abstract

Partial rate factors for the nitration of carboxylic and phosphonic acids PhCH2X and PhCH=CHX (X = C02H or P03H2) have been determined in acetic anhydride and in strongly acidic media. For P-styrylphosphonic acid the rate of bromine addition has been measured and compared with that for cinnamic acid. 13C N.m.r. spectra of the PhX, PhCH2X. and PhCH'CHX systems have been recorded. Substituent effects of the carboxy and phosphonic groups upon the reactivity and upon the shielding of ring carbon atoms are compared and discussed. Close similarity of substituent effects of C02H and P03H2 has been demonstrated. Good correlation between the partial rate factors and 13C chemical shifts has been found for the systems PhX and PhCH2X; in a-styryl derivatives this parallel breaks down owing to the versatile nature of the vinyl group. 270 nm (log E 2.76); for X = CO,H, A , , , , . 273 nm (log E = 2.87) 9]. The available data also allow a comparison of the substituent effects of phosphonic and carboxy groups in aromatic nitration, both in acidic and in aprotic media. Such a comparison, expressed in terms of the relative changes (with respect to benzene) of the free energy of substitution at orthoand meta-positions, is presented in Table 1. The data show that the two substituents produce almost identical selectivity with respect to the orthoand uneta-positions of the ring. This observation rules out immediately any specific ' ortho ' effect in nitration of phenylphosphonic acid, since no decrease in the relative change of the free t The similarity of the electron-acceptor abilities of P(0) (OR), and CO,R, expressed in terms of Taft's o* constants, has been pointed

Experimental and theoretical investigation of the unusual substituent effect of the vinyl group

“…It follows that oPo,H2t = 0.44, similar to that for the carboxylic group (oCO,H+ = 0.42 (14)). Close similarity of substituted effects of groups CO,H and PO,H, has been demonstrated before (15). The excellent correlations in Fig.…”

Substituent effects of phosphorus-containing groups on aromatic reactivity. Determination of substituent constants by 13C nuclear magnetic resonance spectroscopy

“…Substrates 2,3,4,9,10,14,15, and 18 were commercial products and were recrystallized or distilled where necessary. Substrates 1,5,6,7,8,11,12,13,16,and 19 were synthesized according to standard procedures.…”

“…7, and preceding papers of this series), we have used 13C nmr chemical shifts to monitor changes in the electron distribution of the benzene ring in a series of Ph-PZ,,…”

Exploiting in situ NMR to monitor the formation of a metal–organic framework

“…The initial shift to lower ppm over time is consistent with initial aggregation of the linker (as per the control experiments just described and in agreement with conclusions from the SAXS experiments described below), but is also consistent with the direction of anticipated peak shifts on deprotonation of the BTPPA phosphonic acid groups, 41–44 most notably observed in H c at the ortho position with respect to the phosphonic acid substituents. 41,45–47 Subsequent to these two combined effects, and on a more rapid timescale with increasing temperature, a marked swing in the other direction downfield to higher ppm is observed for all the aromatic protons, in line with metal coordination counteracting and exceeding the effects of deprotonation in particular. Significantly, these processes are not observable by simply monitoring nucleation and crystal growth by the other methods outlined in the Introduction above.…”