Results from Carbonyl Stretching Frequencies

The bridging of cyclopentane to form a norbomane system which, according to H. Brown, is also accelerating the solvolysis leads in fact to other results. An increase in angle strain upon the sp - sp transformation in both a cyclopentane and a norbomane system must be essential but nearly the same (for cyclopentanone v o = 1750 cm , for 2-norbomanone v, o = 1751 cm ). At the same time 

In emlo isomer the strongest non-bonded interaction is that between —OTs and 6-endo-H (2.19 A, the sum of the Van der Waals radii being 2.6 A). This interaction decreasing in the transition state should have increased the rate, but the solvolysis rate of endo-brosylate has been shown to be predictable only from the torsional effects. The non-bonded interactions in the ground and the transition state seem to equally destabilize the system and do not, therefore, affect the solvolysis rate of the endo isomer. 

This supports Brown s su estion that 6-endo-hydrogen hinders the detaching of the leaving group from the 2-endo-position but the magnitude of this effect is far less than postulated by Brown. As a model for calculating the solvolysis rates of 

Sulphonate (cm ) 9 GS-TS (kcal) Calc. logio Obs. ogio logiov . - -logi.V J  

This refinement is not relevjmt to the ionization of 2-exo-norbomyl brosylate because the ion generated upon migration of C is an enantiomer of the initial ion. Thus, in this case the anchimeric assistance indicates the formation of an intermediate more stable than the classical 2-cation. Such a particle can evidently be the 2-norbomyl bridged ion 5. 

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The low carbonyl stretching frequency (1689 cm-1) observed in the IR-spectrum is the result of transannular interaction of the C-3 carbonyl group with Nb. Alloechitamine is presumably formed from echitamine chloride by a normal Hofmann elimination, which leads to the enol LVI loss of formaldehyde then gives alloechitamine. The Hofmann stage would be expected to proceed smoothly, as the groups eliminated are situated trans diaxial to the boat-shaped ring. 

Much physical evidence reveals the importance of backbonding. For example, the C-O distance in carbonyl ligands is longer than that in free CO, and the carbonyl stretching frequency is lower than that in free CO. Both of these observations result from the decrease in C-O bond order that results from backbonding. 

The initial impetus to Creger s extensive study of a-anions of carboxylic acids seems to have arisen from attempts to transform steroidal epoxides into y-lactones. Pfeifer has published an extensive paper on the formation and alkylation of such anions. According to MO—LCAO—SCF calculations, the magnitude of the shift of the carbonyl stretching frequency in the i.r. of a-lithio-esters as compared with the non-metalated analogues indicates the degree of ionic character in the C—Li bond the results obtained support a model of a strongly polarized covalent C—Li bond, as opposed to the simple ionic picture. 

The general absorption patterns in the carbonyl region for non-cyclic and cyclic anhydrides are shown in Fig. 9.2. The two bands result from carbonyl interaction, where the in-phase stretch has the higher frequency and the out-... 

These results can again be related to studies of high-surface-area materials. VHien CO is adsorbed on Ti02 after thermoevacuation at elevated temperatures (>770 K), a carbonyl stretching frequency is observed near 2180 cm". Calculations based on an electrostatic model suggest that the frequency must arise from a CO ligand coordinated to Ti sites [20,21]. 

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. 

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