2-butanone conformation

In compound B, the carbon-oxygen distance is close to that predicted for a double bond, 122 pm. Then, the oxygen must be terminal. A structure that conforms to these data is 2-butanone [Fig. 9-37(b)]. 

What products are obtained from the reaction between benzaldehyde and butanone in the presence of base (NaH, room temperature) Draw the structural formulae of all of the reaction products in spatially correct Newman projections. Chose the conformation in which the phenyl and carbonyl groups are antiperiplanar to one another. 

In water, ionization of the C-Br bond occurs first (Ei mechanism) to give the intermediate resonance-stabilized benzylic zwitterion C. After fast rotation about the C-C bond, carbon dioxide leaves conformer D perpendicularly to the plane of the car-benium ion, to give mainly the most stable ( )-isomer of / -bromostyrene. In butanone, after fast rotation about the C-C bond, elimination of CO2 and Br occurs in a concerted single-step (E2 mechanism) for stereoelectronic reasons (Br and C02 must be anti to one another) to give conformer B, which decomposes exclusively to the thermodynamically less stable (Z)-isomer. In more polar solvents, the partly zwitterionic activated complex, leading to zwitterion C in the rate-determining step, will clearly be more stabilized by solvation than the less dipolar activated complex leading directly to the (Z)-isomer of / -bromostyrene from conformer B [851]. 

We present an XPS study of the interfaces P(VDF-TrFE)/Al and P(VDF-TrFE)/PEDOT PSS. As copolymer, we used P(VDF-TrFE) in a molar ratio of 70 30. The material was delivered as film from Piezotech SA, France. As solvent for spin coating, we used 2-butanone. We prepared different concentrations (as wt% P(VDF-TrFE) in 2-butanone) to investigate the dependence on layer thickness. After spin-coating at 6000 rpm, the film was annealed at 135 °C for 2 h to improve the crystallinity of the aXX-trans conformation, the so called P-phase [21]. The thickness of the spin-coated film was measured using a Taylor Hobson (Talystep) profilometer. 

Let us consider the reaction of (S)-3-phenyl-2-butanone, 1. The two conformers of the reactant are la (Eq. 6) and lb (Eq. 7), following the Anh-Felkin modification of Cram s model. The conformer la will predominate over lb because the latter suffers from steric interactions between the two methyl groups that are gauche to each other. The conformers la and lb will generate the products (S,S)-2n and (R, S)-2b, respectively, on reaction with ethyl magnesium iodide. Since la is the predominant conformer, (S,S)-2a is formed as the major product, and (R,S)-2b constitutes the minor product. 

For (R)-3-phenyl-2-butanone, 3, the two reacting Anh-Felkin conformers are 3a and 3b. These conformers are expected to generate predominantly the products (S,... 

The conformational profile for 2-butanone has been developed from analysis of its infrared spectrum. The dominant conformation is anti with a C(1)H and the C(4) methyl group eclipsed with the carbonyl. 

The C(3)-C(4) rotational barrier is 2.48 kcal/mol, similar to the ethane barrier, while the C(l)-C(2) rotational barrier is 0.67kcal/mol. Figure 2.12 shows the rotational potential energy diagram for 2-butanone as calculated at the HF/6-31G level. The preferred conformation of 3-methyl-2-butanone is similar. ... 

The computed (HF/6-31G ) rotational profiles for acetone (2-propanone), 2-butanone, and 3-methyl-2-butanone are given in Figure 2.6P. Draw Newman projections corresponding to each clear maximum and minimum in the curves for each compound. Analyze the factors that stabilize/destabilize each conformation and discuss the differences among them. 

Butanone and other straight chain homologs were examined, and it was calculated that the carbon skeleton prefers an all anti conformation gauche forms are higher in energy, but as with hydrocarbons, not by very much. For 2-butanone, both the structure and the conformational equilibrium were well reproduced (Abe et al., 1969 Pierce et al., 1969). 

Cordova et al. demonstrated in 2005 that the aldol condensation between 4-nitrobenzaldehyde (5 R=p-N02) and cyclic ketones or butanone in the presence of acyclic primary amino acids led to the antz-isomer 6 (Scheme 12.3). One year later, this author described the structure-activity relationship between acyclic amino acids and the aldol derivatives, the synthetic scope of catalysis by acyclic amino acids in aqueous media and water, and studies concerning the reaction mechanism. Excellent enan-tioselectivities (ee up to >99%) were achieved in several cases. As an example of the anh -induction, the (E)-enamine arising from cyclohexanone and the acyclic amino acid could display a proton transfer from the carboxylic acid function to the alkoxide, giving a six-membered chair-like conformation. The favoured approach of the aldehyde would then lead to an anfi-isomer. 

A similar bias is seen in carbonyl compounds. Acetaldehyde shows a 1.0 kcal / mol preference for the eclipsed form over the staggered (Eq. 2.26), with the latter again being a transition state for rotation. In propanal the conformation having the methyl group eclipsed with the carbonyl (Eq. 2.27) is preferred by 1 kcal/mol. Similarly, for 2-butanone and even 3-pentanone, the conformations with the methyls eclipsed with the carbonyl are preferred. It is generally accepted that electronic interactions are controlling these preferences, but the effects are subtle. 

With propanal and 2-butanone it is known that the lowest energy conformation has the methyl group eclipsed with the carbonyl. The calculated relative energies with the other energy minimum (methyl rotated approximately 120° from the carbonyl) by means of ab initio 6-3IG MO theory are... 

The 2,3,3-trimethyl-l-phenyl-l-butanone is an a-substituted ketone, but the a-substituents have no ability to chelate metals. In that case, the role of the Lewis acid will be just to coordinate the oxygen atom, enhancing its reactivity towards the nucleophilic attack. The same open FeUdn-Ahn s model previously commented will be valid for both, TiCU and CeCls-mediated reductions, as it is shown in Scheme 4.4. Again, the first step of the reaction is the coordination of the Lewis acid with the carbonyl group. Although a priori, conformations 9 and 10 could be considered, hydride attack to the carbonyl group in 9 should be favored by steric effects leading to the ti-alcohol 11 as the main reaction product in both cases. 

Further interesting example of NSAIDs, whose fluorescence properties within CD are determined by the mode of inclusion, are nabumetone (10), a naphthalene derivative with a butanone side chain and naproxen (11), a parent propionic acid derivative (Fig. 2). The dominant features of the inclusion of nabumetone inside P-CD are the formation of two conformations of the drug, but the folded structure is the main one, probably due to the presence of water in the proximity of the hydroxyl groups at the gates of CD [59]. This situation... 

---