Protonation studies

Following the classification of Chapter 4.01, three classes will be considered, (a) Compounds isomeric with aromatic compounds (6), (7) and (8). The quaternary, non-aromatic salts (Scheme 7, Chapter 4.01) will be discussed only in connection with protonation studies which lead to the conclusion of their non-existence. The carbonyl derivatives (9), (10), (13) and (14) will also be included here because it is possible to write an aromatic tautomer for each one, (9 )-(14 ), even if it is energetically unfavoured, (b) Dihydro compounds. In this class not only pyrazolines (15), (16) and (17) but also pyrazolidinones (18) and pyrazolinediones like (1) are included, (c) Tetrahydro compounds. Besides the pyrazolidines (19), the pyrazolidinetriones (2) are included here. 

Protonation studies of diphenylphosphinic esters and amides show that Ji>a H i creases upon protonation of the esters but that ypN< h decreases upon protonation of the amides.Values of JpN< ii have been tabulated for a number of compounds. The cyclic aminophosphine (79) has all four Jpxch constants with the same sign, probably positive. Attachment of the proton to an sp carbon atom, as in (80), does not enhance yi>Ncn in fact the reverse occurs. ... 

Large medium effects on the ultraviolet spectra of the protonated form of a number of other amides have been reaffirmed in some recent protonation studies (Farlow and Moodie, 1970 Congdon and Edward, 1972 Barnett and O Connor, 1973). These undoubtedly conceal evidence of tautomeric change. 

Protonation studies of methyl tmd ethyl carbamate [123] and their N-methyl and N,N-dimethyl derivatives (Armstrong and... 

The protonation studies are of interest in another connection. If protonation of metallocenes can be considered to be a simple form of electrophilic attack, it is possible that other types of electrophilic substitution reactions may proceed through initial coordination of the electrophile with the central metal atom (14, 93). The mechanism of acylation of metallocenes may therefore be more complex than might be expected by analogy to similar reactions of benzenoid compounds. Clearly more studies are needed along these lines, better to define specific metal effects on the properties and reactions of these remarkable compounds. 

The carbonyl stretch in xanthone (21) at 1660 cm-1 (58JCS294) can shift to as low a frequency as 1400 cm-1 according to protonation studies. The order of complexing ability of cations towards xanthone suggests that steric factors are of significance (63CJC522). Hydroxyxanthones show characteristic hydroxyl (3300 cm-1) and carbonyl absorption bands (67JCS(C)2500). 

The oxygen and sulfur bases are weaker than the nitrogen bases, and accurate solution basicities are not available. Arnett s heat of protonation studies indicate that the order of decreasing basicity is ROR > ROH > HaO,98 a result that is in agreement with gas-phase measurements.99 Hydrogen sulfide in the gas phase has basicity comparable to that of water (Table 3.18), and substitution of H by alkyl produces stronger gas-phase bases just as does similar substitution on oxygen. 

Molybdenocene dihalides, associated chemistry, 5, 573 Molybdenocene dihydrides monomeric complexes, 5, 568 multimetallic complexes, 5, 570 protonation studies, 5, 570 Molybdenocenes... 

Griend, L. J. V. Verkade, J. G. Pennings, J. F. M. Buck, H. M. Structure-basicity relations among phosphate and phosphite esters. CNDO/2 and protonation studies. /. Am. 

A considerable amount of data on the protonation, and complex formation with metal ions of polymeric amines have been reported. A critical insight leads to the conclusion that much has to be done in order to reach a clear vision of the chemical properties of many polymers of this kind. Most protonation studies deal with the determination of basicity constants with potentiometric techniques, which alone give little information on the protonation mechanism only few studies have been substantiated by spectroscopic (nmr) and calorimetric measurements. 

As mentioned in the previous section, photophysical/chemical investigations are a natural resource regarding aminoalkyl aromatics. In some of these instances, protonation studies have not been on the experimental agenda. The time seems ripe now for the evaluation of these cases for fluorescent PET sensing action... 

---