Acetone protonated

Figure 9 shows MRD profiles for acetone protons in calibrated chromatographic porous glasses (65). The field dependence consists of two logarithmic... 

In principle we could deconvolute the experimental spectrum with the instrumental lineshape, if that were known, to recover the true spectrum. In our example we have some good experimental evidence as to the form of the instrumental lineshape since the acetone signal is (apart from small carbon-13 satellites) a singlet, its experimental shape is just the instrumental lineshape convoluted by a Lorentzian of width l/(7rr2 ), where is the spin-spin relaxation time of the acetone protons. How can we use this experimental evidence to correct the imperfect experimental spectrum The simplest way to deconvolute one function fi uj) by another f2 ( ) is to Fourier transform the ratio of their inverse Fourier transforms ... 

The second step is a nucleophilic attack by the enolate on another molecule of acetone. Protonation gives the aldol product. 

Figure 4.3 An illustration of the impact of humidity on the detection of acetone (protonated signal at m/z 59) and toluene (protonated signal at m/z 93). Panel (a) shows an approximately linear decrease in [HsO ] with humidity and a corresponding linear increase in [HjO (H2O)]. Panel (b) shows the corresponding effects on the protonated acetone and toluene signals and panel (c) shows the response when the humidity effect was included via the factor X. A value oIXm = 0.5, which reflects the relative transmission of H3O (H2O) toHiO, was appropriate for acetone since it reacts with both and HsO (H2O) at roughly the same rate. On...

Removal of an a-hydrogen atom of the ketone as a proton to form n carbauion (acetone anion) ... 

Because the protonation of ozone removes its dipolar nature, the electrophilic chemistry of HOs, a very efficient oxygenating electrophile, has no relevance to conventional ozone chemistry. The superacid-catalyzed reaction of isobutane with ozone giving acetone and methyl alcohol, the aliphatic equivalent of the industrially significant Hock-reaction of cumene, is illustrative. 

A 2-methylthio substituent decreases the basicity of thiazole pK = 2.52) by 0.6 pK unit (269). The usual bathochromic shift associated with this substituent in other heterocycles is also found for the thiazole ring (41 nm) (56). The ring protons of thiazole are shielded by this substituent the NMR spectrum of 2-methylthiothiazole is (internal TMS, solvent acetone) 3.32 (S-Me) 7.3 (C -H) 6.95 (Cj-H) (56, 270). Typical NMR spectra of 2-thioalkylthiazoles are given in Ref. 266. 

Polar solvents shift the keto enol equilibrium toward the enol form (174b). Thus the NMR spectrum in DMSO of 2-phenyl-A-2-thiazoline-4-one is composed of three main signals +10.7 ppm (enolic proton). 7.7 ppm (aromatic protons), and 6.2 ppm (olefinic proton) associated with the enol form and a small signal associated with less than 10% of the keto form. In acetone, equal amounts of keto and enol forms were found (104). In general, a-methylene protons of keto forms appear at approximately 3.5 to 4.3 ppm as an AB spectra or a singlet (386, 419). A coupling constant, Jab - 15.5 Hz, has been reported for 2-[(S-carboxymethyl)thioimidyl]-A-2-thiazoline-4-one 175 (Scheme 92) (419). This high J b value could be of some help in the discussion on the structure of 178 (p. 423). 

Donation of a proton to the reactant often forms a carbenium ion or an oxonium ion, which then reacts ia the catalytic cycle. For example, a catalytic cycle suggested for the conversion of phenol and acetone iato bisphenol A, which is an important monomer used to manufacture epoxy resias and polycarbonates, ia an aqueous mineral acid solution is shown ia Figure 1 (10). 

Pyrroles react with the conjugate acids of aldehydes and ketones to give carbinols (e.g. 67) which cannot normally be isolated but which undergo proton-catalyzed loss of water to give reactive electrophiles (e.g. 68). Subsequent reaction may lead to polymeric products, but in the case of reaction of pyrrole and acetone a cyclic tetramer (69) is formed in high yield. 

The protonated azirine system has also been utilized for the synthesis of heterocyclic compounds (67JA44S6). Thus, treatment of (199) with anhydrous perchloric acid and acetone or acetonitrile gave the oxazolinium perchlorate (207) and the imidazolinium perchlorate (209), respectively. The mechanism of these reactions involves 1,3-bond cleavage of the protonated azirine and reaction with the carbonyl group (or nitrile) to produce a resonance-stabilized carbonium-oxonium ion (or carbonium-nitrilium ion), followed by attack of the nitrogen unshared pair jf electrons to complete the cyclization. 

Increased sensitivity towards acid is observed when protonation occurs on a functional group outside the diazirine ring, giving rise to electron dilution at the carbon atom adjacent to the diazirine carbon. The products isolated are in accord with the proposal (79AHC(24)63) that cation formation at this carbon atom leads to nitrogen extrusion, probably with formation of a vinyl cation. Thus protonated hydroxydiazirine (209) yields acetone, and methylvinyldiazirine (199) on treatment with acids yields butanone (67CB2093). 

Consider protonation of 2-methylpropene (X = CH2) versus protonation of acetone (X = O). 

Fig. 2. The proton magnetic resonance spectrum of 5-nitrobenzofuroxan, in acetone at — Sl C. The bands marked by arrows arise from the 5-nitro tautomer.

Reaction of the cyclopentadienyl rhodium and iridium tris(acetone) complexes with indole leads to the species 118 (M = Rh, Ir) [77JCS(D)1654 79JCS(D)1531]. None of these compounds deprotonates easily in acetone, but the iridium complex loses a proton in reaction with bases (Na2C03 in water, r-BuOK in acetone) to form the ri -indolyl complex 119. This reaction is easily reversed in the presence of small amounts of trifluoroacetic acid. 

---