Iso Propyl groups

The only other C5(i-Pr)5 complex, Mo(Pr5Cp)(CO)3CH3 (30) also shows fluxional iso-propyl groups at 100 °C, but below the coalescence temperature two isomers in the ratio 4 3 are obeserved according to, 3C NMR spectra. They are... 

In terms of chemical stracture, j3-adrenoblockers have much in common. Practically, all of them are derivatives of l-aryloxy-3-aminopropanol-2, the Cj position of which always possesses a substituted or nonsubstituted aromatic or heteroaromatic group connected by an ether bond to a three-carbon chain. An R group at the nitrogen atom of the propanoic region must be represented as either a tertiary butyl group (nadolol, timolol), or an iso-propyl group (the remainder of the drugs). 

Based on the analysis of the reactions in Scheme 3 and on previous studies (46, 47), a mechanism for the reaction was proposed in which the /x-peroxo complex, 16, may simultaneously abstract two hydrogen atoms from iso-propyl groups on the pyrazolyl ligands. Alternatively, because of the weak 0—0 bond, 16 may homolytically dissociate to form two Tp"Co(0-) oxo-radical moieties, and these species would then abstract hydrogen from the iso-propyl groups. In either case, the resulting carbon-centered radical can either react with solvent, as was observed for the Tp complex (46), or with another carbon-centered radical so as to regenerate the Tp"Co(OH) complex and produce a derivative of the Tp" complex with an iso-propenyl substituent, 18. Ultimately, either route would produce the (/x-OH)2 complex, 17. 

If we draw this same intermediate with one of the iso propyl groups drawn out in full we can see that the tertiary hydrogen atom in... 

Another family of inhibitors, hydrogen-donating agents such as iso-propyl and 1,4-di-ivo-propyl benzenes, was investigated by Lamouroux in order to reduce the formation of TBP-TBP dimers, which exhibit a very high plutonium retention of TBP (47). The presence of at least one mobile hydrogen on the iso-propyl group could produce a benzylic tertiary radical stabilized by resonance. The addition of such compounds reduced the concentration of the TBP-TBP dimers by about 50%. 

Answer The large 7ab of the methanol solution is only compatible with both protons being axial. If we assume that the ring is a chair, then the conformation must be as shown in a this is as expected, with the large iso-propyl group being equatorial. The small Jab in benzene solution indicates that both protons are now equatorial the ring has flipped into the other chair form, b. 

A and B are coincident Q and R cannot be reliably distinguished as we are not sure of the preferred conformation of the iso-propyl group. Note the small but characteristic COSY cross peak between the angular methyl P and la. The 14-hydroxyl proton is in slow exchange because it is hydrogen-bonded to the 9,11-epoxide oxygen. 

An alternative model proposed by Northcott and Valenta involves an s-cis conformation of the dienophile as indicated in structure 171 [39]. Shielding of the re face by the iso-propyl group requires a change in the coordination of aluminum to the dienophile oxygen such that the aluminum is coordinated by the oxygen on the same side as the carbon substituent of the aldehyde. This model is consistent with the observation of high induction with dienophiles 159 and 161 in which the conformation is locked s-cis compared with that for dienophile 163 which is locked s-trans (Sch. 17). A combined quantum mechanics-molecular mechanics study has been performed on the... 

Substitution on the C atoms of such amino acid chelates does not give such a pronounced effect. Analogous bis(ethylenediamine) amino acid chelate systems show rather little discrimination between the two diastereoisomers. For example, the ratio of the if and S isomers in the A configuration is about equal for alanine and 2 1 for valine (5). It can be argued that the bulk of the R group is important and that the effect of the iso-propyl group is due to its relative orientation in relation to chelate rings 1 and 2. This effect is related to that of the sarcosinato ion except that the substituent is now more distant from the other chelates and the effect is less. 

Steric factors also play a role. Bulky groups on either R, or R2 decrease the decomposition rate. For example, when an iso-propyl group is substituted for an n-propyl group on R2, the decomposition is five times slower (Table 1). 

The perfluoroalkyl group CF3 has a relatively large van der Waals volume -larger than methyl, mono-fluoromethyl and di-fluoromethyl and between those of the iso-propyl and the tert-butyl groups [35]. The latter is comparable in size to the perfluoro-iso-propyl group. 

Fig. 16.7. The molecular structures of H4Al4(/x -N-i-Pr)4 and H6Al6(/x -N-/-Pr)6, R = i-Pr = isopropyl. Two terminal H atoms and two terminal iso-propyl groups in the latter have been omitted for clarity.

When the t-butyl group (Ra) of terbutryn is replaced by an iso-propyl group (as in ametryn) the binding affinity is decreased by a factor of 3.7 in the wild type. A similar effect is seen for the size of Ra between desmetryn and ametryn. The Iso values of ametryn and atrazine suggested... 

Replacing the methyl groups at the silicon atom of 15 and 17 with bulkier iso-propyl groups was found to increase the ability of comonomer incorporation... 

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