Electronegativity natural

The Q and e values of VP are 0.088 and —1.62, respectively (125). This indicates resonance interaction of the double bond of the vinyl group with the electrons of the lactam nitrogen, whence the electronegative nature. With high e+ monomers such as maleic anhydride, VP forms alternating copolymers, much as expected (126). With other monomers between these Q and e extremes a wide variety of possibiHties exist. Table 14 Hsts reactivity ratios for important comonomers. 

The difference in the properties of the silicon atom from that of the carbon is because of its comparatively bigger size, less electronegative nature and the presence of the available vacant d orbitals. 

The rapid reaction between carboxylic acids and borane is related to the electrophilicity of borane. An acyloxyborane is recognized to be an initial intermediate. The carbonyl group in this molecule, which is essentially a mixed anhydride, is activated by the electronegative nature of the trivalent boron atom. This fact intrigued us greatly and then awoke us interest in whether the acyloxyborane can accept the attack of molecule other than a simple hydride. Addition of 1/3 equiv of borane-TBT complex to the acrylic acid dissolved in dichloromethane followed by diene at low temperature resulted in the formation of Diels-Alder adduct in good yield. Further, the reaction could progress satisfactory even with a catalytic amount of borane. 

Certain aryl and benzyl halides react with primary and secondary amines yielding the corresponding secondary and tertiary amines, in addition to hydrogen halide, much in the same shion as described in section II.B.4. However, by virtue of the electronegative nature of the reagents, the reaction does not proceed further up to quatemisa-tion as with the previous case, neither does it yield quaternary ammonium compounds with tertiary amines. 

This is due to the electronegative nature of the oxygen atom, drawing electron density towards itself, and has a marked effect on the chemical shift of these hydrogens. The hydrogen nuclei are shielded by their electrons from the external magnetic field, but the hydrc en attached to the oxygen is said to be deshielded. 

Williams showed that the heptafiuorobutyryl derivatives of the three unphosphorylated forms of vitamin Bg may be separated by GLC. The highly electronegative nature of the derivatives made electron capture detection suitable for the sensitive assay of the Bg vitamers (152). Patzer and Hilker used N-methyl-bis-trifluoroacetamide (MBTFA) to form derivatives of B vitamers which could be separated by GLC and quantitated by flame ionization detection (153). However, the sensitivity of the flame ionization detector was insufficient to allow quantitation of the Bg vitamers in biological samples. Lim et al. showed that the MBTFA derivatives of B vitamers could be measured at increased sensitivity with a GLC equipped with a N electron capture detector (154). Lim and coworkers used this method to determine the vitamin Be content of bread, skimmed milk, and peas (154). 

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