SYNTHESIS OF HYDROCARBON STANDARDS Tetrahydrofuran (THF) was distilled from sodium/benzophenone under argon atmosphere. 1H- and 13C-NMR spectra were recorded with a Varian INOVA- 400 spectrometer (400 and 100 MHz respectively), as CDCl3 solutions. Chemical shifts are expressed in ppm relative to CDCl3 (7.26 and 77.23 ppm for 1H and 13C NMR, respectively). Mass spectra were obtained with an HP 5890 gas chromatograph interfaced to an HP 5970 MSD, in EI mode (70 eV) with helium carrier gas. The GC was equipped with a DB5-MS column (25 m  0.20 mm ID  0.33 2m film). Products were purified by flash or vacuum flash chromatography using silica gel (230–400 mesh, EM Science, Gibbstown, NJ, USA). All reactions were carried out in dried flasks under a positive atmosphere of argon. Crude solutions of products were dried over anhydrous Na2SO4 and concentrated by rotary evaporation under partial vacuum. (n-Alkyl)triphenylphosphonium Bromides. Nonyl-, tetradecyl-, and hexa- decyltriphenylphosphonium bromides were obtained from Lancaster Synthesis (Pelham, NH, USA). Other phosphonium salts were synthesized as follows. A solution of triphenylphosphine (1.73 g, 6.6 mmol) and 1-bromoeicosane (2.38 g, 6.6 mmol; TCI America, Portland, OR, USA) in toluene (3.5 ml) was refluxed under argon for 7 d. After cooling, the mixture was poured into hexane (30 ml) with vigorous stirring. After 30 min, the suspension was allowed to settle and solvent was decanted. Hexane (30 ml) was added and the resulting suspension was stirred for 1 hr. The precipitated phosphonium salt was filtered with a Bu¨chner funnel under argon, rinsing repeatedly with hexane, and dried under vacuum for 10 hr, affording 3.69 g of product (89.5% yield). (n-Octadecyl)triphenylphosphonium bromide was prepared in analogous fash- ion from octadecyl bromide (Aldrich Chemical Co., St. Louis, MO, USA). Synthesis of Straight-chain Z-alkenes. Aldehydes needed for Wittig reactions that were not commercially available were produced by oxidation of the corresponding alcohols with 1.2 equivalents of pyridinium chlorochromate (PCC) and an equal weight of powdered 4A˚ molecular sieve in CH2Cl2. The mixtures were stirred 45–60 min at room temperature, then diluted with 5 volumes of hexane, stirred 15 min to allow precipitation, and filtered through Celite. The resulting solutions of crude aldehydes were concentrated, then taken up in THF and used immediately. The synthesis of (Z)-13-nonacosene is representative. A mixture of hexadecyltriphenylphosphonium bromide (5.67 g, 10 mmol) in 50 ml of THF was cooled in an ice-bath, and sodium hexamethyldisilazide (1 M in THF, 12 ml, 12 mmol; Lancaster Synthesis) was added dropwise. The resulting orange mixture was stirred 1 hr at 0-C, then a THF solution of freshly prepared tridecanal (10 mmol) was added dropwise and the mixture was allowed to slowly warm to room temperature overnight. The mixture was quenched with 1 M aqueous HCl and extracted with hexane. The hexane layer was washed with brine, dried, concentrated, and purified by vacuum flash chromatography, eluting with hexane. The resulting colorless liquid (3.57 g) was purified further by recrystallization from 100 ml acetone at j20-C, filtering in a cold room, producing (Z)-13-nonacosene (2.71 g) as a low-melting white solid. The stereo- chemical purity was determined to be >96% Z by epoxidation followed by GC- MS analysis. The resulting two epoxides were separated to baseline, with the minor, trans epoxide eluting first. Z9:C29, Z14:C29, Z13:C31, Z14:C31, and Z15:C31 were obtained by analogous procedures, using the appropriate phosphonium salts and aldehydes, with similar purities and yields. Preparation of 2-Alkanones. A solution of 2-hexadecanol (2.00 g, 8.2 mmol) in dry CH2Cl2 (6 ml) was added dropwise to a suspension of PCC (2.13 g, 9.9 mmol) and powdered 4A˚ molecular sieve (2.13 g) in CH2Cl2 (10 ml) at room temperature and stirred overnight. Ethyl ether (50 ml) was added and the resulting mixture was filtered through a pad of 1 cm of Celite (bottom layer) and 1 cm of silica, rinsing the pad with ether. After concentration, the residue was purified by vacuum flash chromatography (hexane: ethyl acetate, 9:1) affording 2-hexadecanone (1.88 g) in 95% yield. 1H NMR: d 0.87 (t, 3H, J = 7.0 Hz), 1.2– 1.34 (m, 22H), 1.55–1.70 (m, 2H), 2.13 (s, 3H), 2.41 (t, 2H, J = 7.6 Hz). 13C NMR: d 14.35, 22.92, 24.10, 29.41, 29.58, 29.63, 29.70, 29.83, 29.87 (2C), 29.89, 29.91, 30.07, 32.15, 44.06, 209.66. MS m/z 240 (M+, 3), 225 (2), 197 (1), 183 (1), 153 (1), 139 (1), 127 (2), 113 (2), 96 (9), 95 (11), 71 (37), 59 (57), 58 (100), 57 (18), 43 (97), 41 (32). 2-Tetradecanone (83%) was prepared in analogous fashion from 2- tetradecanol. 1H NMR: d 0.87 (t, 3H, J = 7.0 Hz), 1.20–1.34 (m, 18H), 1.50– 1.62 (m, 2H), 2.13 (s, 3H), 2.41 (t, 2H, J = 7.6 Hz). 13C NMR: d 14.34, 22.91, 24.10, 29.41, 29.57, 29.62, 29.69, 29.82, 29.85, 29.87, 30.07, 32.13, 44.06, 209.68. MS m/z 212 (M+, 3), 197 (1), 169 (1), 154 (2), 127 (2), 113 (2), 96 (6), 85 (9), 71 (33), 59 (44), 58 (100), 57 (16), 43 (97), 41 (34). Methyl-branched Alkenes. (n-Octadecyl)triphenylphosphonium bromide (1.79 g, 3.0 mmol) was suspended in THF (6 ml) and lithium diisopropyla- mide (LDA, 1.5 M in cyclohexane, 2.1 ml, 3.15 mmol) was added dropwise at j10-C. The mixture was stirred for 3 hr and then cooled to j30-C, and 2-dodecanone (0.553 g, 3.0 mmol) in THF (1.5 ml) was added dropwise. The resulting mixture was allowed to warm to room temperature, stirred overnight, then quenched with water and poured into saturated aqueous NH4Cl solution. The organic layer was separated and the aqueous phase was extracted with diethyl ether (3  20 ml). The combined organic layers were washed with brine, dried, and concentrated. The residue was purified by vacuum flash chromatog- raphy (hexane), affording (11E/Z)-11-methylnonacosene (0.83 g, 66%), in a 55/ 45 ratio of geometric isomers. MS: m/z 420 (M+, 8), 294 (7), 279 (6), 209 (2), 182 (6), 167 (16), 153 (5), 139 (10), 125 (16), 111 (35), 97 (61), 83 (54), 69 (63), 57 (100), 55 (79), 43 (84), 41 (55). Analogous reactions between the appropriate methylketones and Wittig reagents were used to make the following compounds: (9E/Z)-9-Methylnonacosene (50%), 54/46 ratio of geometric isomers. MS: m/z 420 (M+, 8), 322 (6), 307 (6), 266 (2), 207 (3), 195 (2), 181 (2), 167 (4), 154 (10), 139 (26), 125 (13), 111 (36), 97 (59), 83 (60), 69 (74), 57 (100), 55 (86), 43 (88), 41 (53). (13E/Z) 13-Methylnonacosene (44%), 55/45 ratio of isomers. MS: m/z 420 (M+, 8), 266 (7), 251 (7), 210 (9), 195 (11), 181 (3), 167 (5), 153 (5), 139 (10), 125 (19), 111 (38), 97 (59), 83 (53), 69 (68), 57 (100), 55 (86), 43 (84), 41 (55). (15E/Z)-15-Methylnonacosene (46%), 55/45 ratio of isomers. MS: m/z 420 (M+, 8), 238 (13), 223 (17), 182 (9), 167 (3), 153 (8), 139 (11), 125 (21), 111 (43), 97 (63), 83 (58), 69 (69), 57 (100), 55 (89), 43 (83), 41 (58). (7E/Z)-7-Methylpentacosene (40%), 53/47 ratio of isomers. MS: m/z 364 (M+,11), 294 (6), 279 (6), 266 (4), 238 (3), 182 (1), 167 (4), 153 (6), 139 (7), 126 (12), 125 (12), 111 (50), 97 (50), 83 (61), 69 (83), 57 (94), 55 (100), 43 (85), 41 (67). (11E/Z)-11-Methylpentacosene (54%), 64/36 ratio of isomers. MS: m/z 364 (M+, 12), 238 (7), 223 (8), 182 (12), 167 (12), 153 (5), 139 (9), 125 (17), 111 (39), 97 (66), 83 (59), 69 (78), 57 (98), 55 (100), 43 (90), 41 (71). (13E/Z)-13-Methyluntriacontene (39%), 55/45 ratio of isomers. MS: m/z 448 (M+, 6), 294 (7), 279 (5), 266 (4), 210 (7), 195 (11), 182 (5), 167 (4), 153 (5), 139 (10), 125 (18), 111 (36), 97 (58), 83 (52), 69 (63), 57 (100), 55 (78), 43 (82), 41 (47). (15E/Z)-15-Methyluntriacontene (52%), 54/46 ratio of isomers. MS: m/z 448 (M+, 6), 266 (7), 251 (8), 238 (10), 223 (8), 210 (7), 182 (5), 167 (5), 153 (7), 139 (12), 125 (19), 111 (39), 97 (58), 83 (53), 69 (63), 57 (100), 55 (80), 43 (87), 41 (50). Methyl-branched Alkanes. (11E/Z)-11-Methylnonacosene (0.810 g, 1.92 mmol) in hexane (10 ml) was reduced with hydrogen and 5% Pd/C (0.080 g) catalyst for 16 hr. The mixture was filtered through Celite and concentrated to afford 11-methylnonacosane (0.802 g, 98.5% yield). 1H NMR: d 0.83 (d, 3H, J = 6.4 Hz), 0.88 (t, 6H, J = 7.0 Hz), 1.00–1.14 (m, 2H), 1.16–1.40 (m, 51H). 13C NMR: d 14.37, 19.96, 22.93, 27.32, 29.60, 29.90, 29.94, 29.97, 30.27, 32.17, 32.97, 37.33. MS: m/z 407 (M-15, 1), 393 (1), 281 (10), 280 (11), 252 (3), 169 (13), 168 (30), 155 (3), 141 (4), 140 (5), 127 (8), 113 (13), 99 (21), 85 (57), 71(74), 57 (100), 43 (58).