Carbon-17 chain, unsaturation

Monohydnc alcohols are named by adding -01 to a molecular skeleton name. Carbon chains, unsaturation, etc., are numbered in a manner analogous to that used for carboxylic adds. (See preceding section.)... 

Additional factors controlling the rate of decomposition include carbon chain unsaturation, which increases rate of decomposition, number, and position of Cl atoms on an aromatic ring. For example, 2,4-dichlorophenoxyacetic acid is degraded readily, whereas 2,4,5-trichlorophenoxyacetic acid is more resistant. Finally, the position of attachment of a side chain alters the decomposition rate of aromatic compounds. For... 

Unsaturated Hydrocarbons. Olefins from ethylene through octene have been converted into esters via acid-catalyzed nucleophilic addition. With ethylene and propjiene, only a single ester is produced using acetic acid, ethyl acetate and isopropyl acetate, respectively. With the butylenes, two products are possible j -butyl esters result from 1- and 2-butylenes, whereas tert-huty esters are obtained from isobutjiene. The C5 olefins give rise to three j iC-amyl esters and one /-amyl ester. As the carbon chain is lengthened, the reactivity of the olefin with organic acids increases. 

A similar pre-orientation involving unsaturated carbon chains was operative on generating twelve-membered enediyne 23 and arenediyne lactams 24 [7]. The seco methylesters 21 and 22 were cleaved with LiOH, the corresponding carboxylic acids underwent cyclizations after activation with 2-fluoro-pyridinium tosylate 25 [8]. Dimerization products were found as by-products (<10%). It should be pointed out, that the lactamization succeeded in a single step in about 75% yield by treating the seco-methylesters 21 and 22 with Me3Al in refluxing methylene chloride. Obviously, the latter route was more convenient (Scheme 5). 

The classification is unaffected by allylic, vinylic, or acetylenic unsaturation appearing in both starting material and product, or by increases or decreases in the length of carbon chains for example, the reactions f-BuOH f-BuCOOH, PhCHgOH - PhCOOH, and PhCH=CHCH20H -PhCH=CHCOOH would all be considered as preparations of carboxylic acids from alcohols. Conjugate reduction and alkylation of unsaturated... 

The carbon chains of samrated fatty acids form a zigzag pattern when extended, as at low temperamres. At higher temperatures, some bonds rotate, causing chain shortening, which explains why biomembranes become thinner with increases in temperamre. A type of geometric isomerism occurs in unsaturated fatty acids, depending on the orientation of atoms or groups around the axes of double bonds, which do not allow rotation. If the acyl chains are on the same side of the bond, it is cis-, as in oleic acid if on opposite sides, it is tram-, as in elaidic acid, the tram isomer of oleic acid (Fig-... 

Finaiiy, carbon chains that have an unsaturated bond, an aromatic ring or another group, can cause dangerous reactions which involve these structural elements or groups. In this case, the simultaneous presence of these structural parameters can boost their reactivity due to the electronic effects that they exert on each other. 

II. Boron-Carbon Multiple Bonding in Open-Chain Unsaturated Organo-... 

BORON-CARBON MULTIPLE BONDING IN OPEN-CHAIN UNSATURATED ORGANOBORANES... 

OH,46-49-51,57 cclj44 C10,58 CNj47 NHj47 CHg52 Nh2,56 small Si- and Ge-containing species,54 and unsaturated carbon chain species.55... 

Figure 5.16 Photoactivation of a phenyl azide group with UV light results in the formation of a short-lived nitrene. Nitrenes may undergo a number of reactions, including insertion into active carbon-hydrogen or nitrogen-hydrogen bonds and addition to points of unsaturation in carbon chains. The most likely route of reaction, however, is to ring-expand to a dehydroazepine intermediate. This group is highly reactive toward nucleophiles, especially amines.

Some proteins can be posttranslationally modified by the addition of prenyl groups. Prenyl groups are long-chain, unsaturated hydrocarbons that are intermediates in isoprenoid synthesis. The farnesyl group has 15 carbons, and the geranylgeranyl has 20 carbons. They are attached to a cysteine residue near the end of the protein as a thiol ether (Protein-S-R). Other proteins can have a long-chain fatty acid (C14=myristoyl, C16=palmitoyl) attached to the amino terminus as an amide. These fatty acid modifications can increase the association of proteins with the membrane. 

Stannanes bearing aliphatic groups with unsaturation in the carbon chain are grouped in Table 3, including both open-chain and cyclic vinyl-, allyl- and alkynylstannanes. 

In contrast to pheromones that involve single complex compounds, many moth species have been found to utilize a specific blend of relatively simple fatty acid-derived compounds. It appears that the evolution of a unique enzyme, A1 desaturase, used in combination with 2-carbon chain-shortening reactions (Figure 3) has allowed moth species to produce a variety of unsaturated acetates, aldehydes, and alcohols that can be combined in almost unlimited blends to impart species specificity. For example, biosynthetic precursors for the six-component pheromone blend of acetates for the cabbage looper moth (12) (Figure 2) can be determined easily from the cascade of acyl intermediates produced by the A11-desaturase and chain-shortening reactions (Figure 3). 

Fatty acids are carboxylic acids, often with a long aliphatic tail (long carbon chains), which can be either saturated (all single bonds) or unsaturated. They are biosynthesized from two-carbon units (acetate, CH3COO ), and therefore usually have an even number of carbons with a range of C4 to C36, although Ci6 and Ci8 are dominant. Figure 7.7 shows the structure of octadecanoic acid (slearic acid, Ci8 o), c/.v-9-octadeccnoic acid (oleic acid, Ci8 i), and... 

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