A Fenchone

The mechanism follows the usual path cyclization of linalyl diphosphate, followed by attack of the n electrons of the second double bond, produce an intermediate carbocation. A carbocation rearrangement occurs, and the resulting carbocation reacts with water to form an alcohol that is oxidized to give a-fenchone. 

Fenchone is a pleasant-smelling terpene isolated from oil of lavender. Propose a pathway for the formation of a-fenchone from geranyl pyrophosphate. Hint A car-bocation rearrangement is required.)... 

Oil of Cedar Leaf. Cedar leaf oil. Obtained by steam distillation from the fresh leaves of Thuja occidentalis L, Cupressaceae. Although this oil is known commercially as cedar leaf oil, the tree from whose leaves it is obtained is not a true cedar it is a coniferous tree popularly known as "arbor vitae, sometimes erroneously called white cedar. Habit. Canada and Northern U.S. Constit. o-pinene, d-ikujone, a -fenchone. 

Pine Oil. This oil is obtained by extraction and fractionation or by steam distillation of the wood of Pinuspalustris Mill, and other species. Most of the oil is produced ia the southeastern United States. The composition of the oil depends on the fractions chosen, but the chief constituents are terpene alcohols, mainly terpiaeol. Piae oil finds use as a germicide ia disiafectants and soaps as an ingredient ia iasecticides, deodorants, poHshes, sweepiag compounds, and catde sprays and as raw material for the manufacture of perfumery-grade terpiaeol [8000-41 -7], anethole [104-46-1], fenchone (137), and camphor (35). 

By using d-fenchone a D-Z-fenchene was prepared, having an optical rotation — 32°, and yielding a dibromide melting at 87° to 88°. -... 

Bertram and Helle some years ago prepared a fenchene, which they termed isofenchene, by splitting off water from isofenchyl alcohol. L-d-fenchene prepared from Z-fenchone in a similar manner was found to have an optical rotation - 29°. 

The chemistry of fenchyl alcohol, Cj HjgO, must be regarded as in a somewhat unsettled state, as questions of isomerism arise which are as yet unsolved. It was ori nally prepared by Wallach by reducing the ketone fenchone, a natural constituent of several essential oils, by means of sodium. Later he obtained it in fairly large quantities as a byproduct in the preparation of fenchone-carboxylic acid, by passing a current of C(X through an ethereal solution of fenchone in the presence of sodium. Fenchyl alcohol has, so far, been found in one essential oil only, namely, that of the root wood of Pinus palustris. 

Pickard, Lewcock and Yates have prepared fenchyl alcohol by the reduction of laevo-rotatory. On conversion into its hydrogen phthalate and fractionally crystallising the magnesium and cinchonine salts, they obtained a fraction, which on saponification yielded Za w-fenchyl alcohol, having a specific rotation of - 15 5°, which is probably the correct value for this figure. 

Fenchyl alcohol yields a phenylurethane melting at 88° when prepared from the optically inactive alcohol, and at 82-5° when prepared from the optically active form. It yields fenchone on oxidation, which can be identified by its crystalline combinations (vide fenchone). 

When the terpene a-fenchene (isopinene) is hydrated by means of acetic and sulphuric acids, it yields an isomer of fenchyl alcohol, which is known as isofenchyl alcohol (q.v.), and which on oxidation yields iso-fenchone, as fenchyl alcohol yields fenchone. The two ketones, fenchone and isofenchone, are sharply differentiated by isofenchone yielding iso-fenchocamphoric acid, Cj Hj O, on oxidation with potassium permanganate, which is not the case with fenchone. According to Aschan,i the hydrocarbon found in turpentine oil, and known as /9-pinolene (or cyclo-fenchene—as he now proposes to name it), when hydrated in the usual manner, yields both fenchyl and isofenchyl alcohols, which on oxidation yield the ketones fenchone and isofenchone. According to Aschan the relationships of these bodies are expressed by the following formulae —... 

The most characteristic derivative for the identification of fenchone is its oxime. Five grams of fenchone are dissolved in 80 c.c. of absolute alcohol and a solution of 11 grams of hydroxylamine hydrochloride in 11 C.C. of boiling water containing 6 grams of caustic potash, is added. After a time the oxime separates in the form of fine crystals which on recrystallisation from alcohol melt at 164° to 165° (active form) or 158° to 160° (inactive form). 

Figure 14. The C li core region XPS of fenchone recorded with a photon energy hv = 308.5eV. Included in the figure are bars indicating calculated AExxCPWSh — PW9I) + Qa core-binding energies. Data taken from Ref. [38]. The inset shows the structure of the (1S,4/ )-enantiomer.

The well-resolved C=0 li peak in the fenchone XPS provides an excellent opportunity to examine PECO from a single, well-characterized initial orbital. As has been previously mentioned, it might be thought that such a localized, spherically symmetric initial orbital would not be sensitive to the molecular enantiomer s handedness, but as can be seen in Fig. 15 (a) the dichroism in the electron yield recorded at the magic angle is sufficiently large to be easily visible by eye as a difference in the intensity of the Icp and rep spectra. 

Figure 15. Circular dichroism of the C=0 C li peak (BE = 292.7 eV) in fenchone at three different photon energies, indicated, (a) Photoelectron spectrum of the carbonyl peak of the (1S,4R) enantiomer, recorded with right (solid line) and left (broken line) circularly polarized radiation at the magic angle, 54.7° to the beam direction, (b) The circular dichroism signal for fenchone for (1R,4A)-fenchone (x) and the (lS,41 )-fenchone (+) plotted as the raw difference / p — /rep of the 54.7° spectra, for example, as in the row above, (c) The asymmetry factor, F, obtained by normalizing the raw difference. In the lower rows, error bars are included, but are often comparable to size of plotting symbol (l/ ,4S)-fenchone (x), (lS,4R)-fenchone (+). Data are taken from Ref. [38],...

In this instance, the (5)-enantiomer data have been negated prior to plotting. From previous discussion of the antisymmetry of the parameters under enantiomer exchange (e.g., Section III.A) it is recognized that it is then to be expected that the (R)- and (5)-enantiomer data should fall on the same experimental trend line. That they do indeed do so shows, as was argued in the Section IV.A for fenchone, that the behavior is at least qualitatively in accord with a pure electric dipole model. Furthermore, combining two distinct data sets [(/ )- and (5)-enantiomers] in this manner provides a consistency check on the reproducibility of the PECD data. It seems good practice to include measurement of both enantiomers, where this is feasible, in an experimental study. 

Eugenol, ml08 Eugenol methyl ether, a84 Fenchone, t376 Fenchyl alcohol, t375 A -9/7-(2-Fluorenyl)acetainide, al3... 

---