R Stretching Frequencies

Hammen equation A correlation between the structure and reactivity in the side chain derivatives of aromatic compounds. Its derivation follows from many comparisons between rate constants for various reactions and the equilibrium constants for other reactions, or other functions of molecules which can be measured (e g. the i.r. carbonyl group stretching frequency). For example the dissociation constants of a series of para substituted (O2N —, MeO —, Cl —, etc.) benzoic acids correlate with the rate constant k for the alkaline hydrolysis of para substituted benzyl chlorides. If log Kq is plotted against log k, the data fall on a straight line. Similar results are obtained for meta substituted derivatives but not for orthosubstituted derivatives. 

Tertiary pyrrolines (49, = 1) and piperideines (49, = 2) (if R = H and the enamine can exist in the monomeric form or if R = aryl) evidently possess an endocyclic -double bond (79,155,156). The stretching frequency of the double bond can be lowered to 1620-1635 cm by conjugation with an aromatic substituent. The double bond of an analogous compound with aliphatic substituents in position 2 may occupy either the endo or the exo position. Lukes and co-workers (157) have shown that the majority of the five-membered-ring compounds, traditionally formulated with the double bond in a position, possess the structure of 2-alkylidene derivatives (50) with an exocyclic double bond, infrared absorption at 1627 cm . Only the 1,2-dimethyl derivative (51) is actually a J -pyrroline, absorbing at 1632 cm . For comparison, l,3,3-trimethyl-2-methylene pyrrolidine (52) with an unambiguous exocyclic double bond has been prepared (54). 

Carbonyl stretching frequency in 2-acetyl-5-R-thiophenes CCI4 0.0075 0.001 0.002 0.951 6 k... 

Relationships between the carbon-oxygen stretching frequencies of carboxylato complexes and the type of carboxylate coordination. G. B. Deacon and R. J. Phillips, Coord.. Chem. Rev., 1980, 33, 227-250 (177). 

Consider first that the atom of R bonded to H or D is carbon. An aliphatic C-H bond has a typical stretching frequency of 8.7 X 1013 s 1 or 2900 cm-1. Substitution into Eq. (9-96) gives... 

Kinetic isotope effect. Calculate the kie for R-H/R-T and R-D/R-T, taking for a carbon-hydrogen bond a stretching frequency of 2900 cm 1. 

As expected, [TpBut,Me]Zn(i71-0C02Me) [1689 and 1280 cm-1] and [TpButMe]Zn(T71-0C02H) [1675 and 1302 cm-1] exhibit similar r(CO) stretching frequencies, indicative of similar binding modes for the (0C02H) and (0C02Me) ligands. 

Dioxygen and its ions can bind in mononuclear and dinuclear structures in a number of ways,962 as illustrated in Scheme 1. The typical reaction of dioxygen with Co compounds involves a number of these binding forms, outlined in Scheme 2. Mononuclear Co111—peroxo complexes are relatively rare, but yellow trigonal bipyramidal complexes [Co(02)L2]+ (L = chelating phosphines dppe or dppp) have been characterized structurally where the 022 is bonded to the Co in the side-on r]2 form (Co—O 1.858(7) 1.881(4) A), with O—O stretching frequencies ( 870 cm-1) consistent with Coin-peroxo speciation.963... 

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