Pinene protonation

Figure 1.17 Section ofthe H, H NOESY showing the contacts from the ortho P-phenyl protons to various p-pinene protons. Chiraphos = Ph2pCH(CH3)CH(CH3)PPh2.

Figure 2.11. Proton-Proton shift correlations of a-pinene (1) [purity 99 %, CDCls, 5 % v/v, 25 °C, 500 MHz, 8 scans, 256 experiments], (a) HH COSY (b) HH TOCSY (c) selective one-dimensional HH TOCSY, soft pulse irradiation at Sh = 5.20 (signal not shown), compared with the NMR spectrum on top deviations of chemical shifts from those in other experiments (Fig. 2.14, 2.16) arise from solvent effects...

The pulse sequence which is used to record CH COSY Involves the H- C polarisation transfer which is the basis of the DEPT sequence and which Increases the sensitivity by a factor of up to four. Consequently, a CH COSY experiment does not require any more sample than a H broadband decoupled C NMR spectrum. The result is a two-dimensional CH correlation, in which the C shift is mapped on to the abscissa and the H shift is mapped on to the ordinate (or vice versa). The C and //shifts of the //and C nuclei which are bonded to one another are read as coordinates of the cross signal as shown in the CH COSY stacked plot (Fig. 2.14b) and the associated contour plots of the a-plnene (Fig. 2.14a and c). To evaluate them, one need only read off the coordinates of the correlation signals. In Fig. 2.14c, for example, the protons with shifts Sh= 1.16 (proton A) and 2.34 (proton B of an AB system) are bonded to the C atom at c = 31.5. Formula 1 shows all of the C//connectivities (C//bonds) of a-pinene which can be read from Fig. 2.14. 

HC HMQC (heteronuclear multiple quantum coherence) and HC HSQC (heteronuclear single quantum coherence) are the acronyms of the pulse sequences used for inverse carbon-proton shift correlations. These sensitive inverse experiments detect one-bond carbon-proton connectivities within some minutes instead of some hours as required for CH COSY as demonstrated by an HC HSQC experiment with a-pinene in Fig. 2.15. 

Figure 2.15. HC HSQC experiment (contour plot) of a-pinene [ CDCI3, 5 % v/v, 25 °C, 125 MHz for C, 500 MHz for h, 4 scans, 256 experiments]. This experiment gives the same information as Fig. 2.14 within 8 minutes instead of two hours required for the CH-COSY in Fig. 2.14 due to higher sensitivity because of proton detection and stronger magnetic field. Deviations of proton shifts from those in Fig. 2.14 arise from the change of the solvent. The methylene protons collapsing in Fig. 2.14 at Sh = 2.19 (200 MHz) display in this experiment an AB system with = 2.17 and Sg = 2.21 (500 MHz)...

By a ten-step route ftom a-pinene [7], (15)-(-)-cxo-2,4-dideutero-apopinene was synthesized thrice with different deuterium concentrations. The hydrogen contents (19%, 15.1%, and 6.1%) of the molecules at the C2 position were determined by 200 MHz proton... 

Although the monoterpene camphor occurs naturally, substantial amounts are produced semi-synthetically from a-pinene, a component in turpentine. Treatment of a-pinene with aqueous HCl protonates the double bond by an... 

Figure 1.16 H, H NOESY spectrum of 80. The cross peaks indicated by the arrows arise from selective interligand NOE effects, i.e., the ortho protons of the bipyridyl recognize the p-pinene...

This NOE idea was then extended to Pd(ii) allyl complexes with bidentate phosphine auxiliaries [99-111], with the ortho P-phenyl protons acting as the reporters (see 81). Figure 1.17 shows a section of the H, H NOESY for [Pd(P-pinene allyl) (Chiraphos)](OTf) (Chiraphos = Ph2PCH(CH3)CH(CH3)PPh2), 81 [129], and reveals the numerous contacts from the chiral phenyl array to the allyl ligand. 

Several additional studies were carried out to obtain information about the precise behavior of the various components in the model system. The interplay between the manganese porphyrin and the rhodium cofactor was found to be crucial for an efficient catalytic performance of the whole assembly and, hence, their properties were studied in detail at different pH values in vesicle bilayers composed of various types of amphiphiles, viz. cationic (DODAC), anionic (DHP), and zwitterionic (DPPC) [30]. At pH values where the reduced rhodium species is expected to be present as Rh only, the rate of the reduction of 13 by formate increased in the series DPPC < DHP < DODAC, which is in line with an expected higher concentration of formate ions at the surface of the cationic vesicles. The reduction rates of 12 incorporated in the vesicle bilayers catalyzed by 13-formate increased in the same order, because formation of the Rh-formate complex is the rate-determining step in this reduction. When the rates of epoxidation of styrene were studied at pH 7, however, the relative rates were found to be reversed DODAC DPPC < DHP. Apparently, for epoxidation to occur, an efficient supply of protons to the vesicle surface is essential, probably for the step in which the Mn -02 complex breaks down into the active epoxidizing Mn =0 species and water. Using a-pinene as the substrate in the DHP-based system, a turnover number of 360 was observed, which is comparable to the turnover numbers observed for cytochrome P450 itself. 

The /3-pinene fraction was used as a reference to determine the isomerization activity of the supports. Results given in Table 4 show that carbon VII is particularly inert with respect to /3-pinene. This behaviour is certainly related to the high content of this carbon in potassium (0.5 wt.-%). On the contrary, the CaO impurities present in carbon V seem to increase the isomerization activity of this carbon. It is well-known that the double bond shift isomerization of hydrocarbons can proceed via carbocation intermediates (protonic catalysis) or via allylic carbanion intermediates (acido-basic or purely basic catalysis) [Ref.7]. The results obtained with potassium-doped carbons show that in /3-pinene isomerization during HDS, the protonic mechanism predominates. 

Sorensen and co-workers799-801 have studied the fate of observable camphene hydrocation 190 prepared from isoborneol 187, camphene 188, or tricyclene 189 in HSO3F acid medium (Scheme 5.74). The intermediate cycloalkenyl cation 191 can also be prepared by protonation of a-terpineol (192), sabine (193), and /3-pinene (194) (Scheme 5.75). 

Answer The p-pinene molecule is small, roughly spherical and lacking in polar functional groups. It can therefore tumble very rapidly in solution without perturbing surrounding solvent molecules. This rapid tumbling leads both to inefficient proton relaxation by the dipole-dipole mechanism, so that NOEs are too small to measure easily ( 6.2.1 and 6.4.3), and to relatively slow deuterium relaxation, which gives sharp deuterium lines ( 7.2.3). 

In the case of /J-pinene (Fig. 13), it is proposed that the protonic initiation creates a cyclic tertiary carbenium ion which rearranges into a more stable pendant species, and the successive addition-isomerization processes lead to a chain structure with alternating isobutyl and cyclohex-enyl subunits. The presence of one unsaturation per repeating unit has been confirmed by polymer analysis. 

Good yields of 1 1 adducts have also been obtained from Lewis acid catalyzed reactions of methyl chloropropiolate or DMAD with alkenes. With methyl chloropropiolate, cyclobutenes are obtained exclusively from mono- and 1,2-di-substituted alkenes and mixtures of ene adducts and cyclobutenes are obtained with 1,1-di-, tri- and tetra-substituted alkenes. With DMAD, ene adducts are obtained exclusively from 1,1-di-, tri- and tetra-substituted alkenes and mixtures of ene adducts and cyclobutenes are obtained hrom 1,2-disubstituted alkenes. EtAlCb is a more effective catalyst than AlCb since it is a proton scavenger as well as a Lewis acid. With AlCb, lactone byproducts are also formed. - The relative reactivity of alkenes in these Lewis acid catalyzed reactions was found to be 1,1-di- > tri- > tetra- mono- > 1,2-di-substituted. With reactive ene components such as methylenecyclohexane, ethyl-idenecyclohexane and -pinene, good yields of ene adducts can be obtained with DMAD by thermal reaction at 110-130 "C for 0.25-6 d. ... 

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