Double bonds attached

Because the extension of the polaron in polyene radical cations is finite (10-20 double bonds depending on the type of calculation), its electronic structure is independent of the number of double bonds attached to either side of it, so that the two lines in Figure 29 must bend at some point to meet the abscissa horizontally, as indicated by the dashed curves. Apparently, the point of inflection has not been reached for n = 15, but it is of interest that the curve for the first excited state could well extrapolate to 0.35 eV, which happens to be where the absorption of a polaron in polyacetylene has been observed300. If this is true, a second, more intense absorption band should occur between 0.5 and 0.7 eV, but the corresponding experiments have not yet been carried out. 

Reactivity Benzene does not undergo reactions typical of compounds with double bonds. For example, when ethene is bubbled through bromine water (bromine dissolved in water), the solution is decolorized as the Br2 molecules attack the double bond, attach to the molecule, and form dibromoethane (Fig. 2.7). Benzene does not decolorize bromine water. 

Rule 9. Indicate the position of each double bond within the ring structure by only the number of the lower-numbered carbon to which the double bond is attached — e.g, bicycloQ3.1.0 ]hex-2-ene, 2,4-norcaradiene, 3-norpinene. If double bonds attach substituents to the rings or are present in the substituent groups, their presence is denoted in the names of the substituent groups — e.g., the systematic name for sabinene (Formula 49, Chart 10) is l-isopropyl-4-methylenebicycloQ3.1.0 hexane the nor- name, which is the recommended name, for nopadiene (Formula 64, Chart 12) i s 6,6-dimethyl- 2-vinyl- 2-norpinene. 

Rule 7. If a double bond attaches a substituent to the nor- ring, its presence is denoted by the name of the substituent group preceded by the proper ring position number, and the structure is named as a norbornane derivative - e.g., 2-methylene-norbornane. 

This reaction is exothermic by 8.6 kJ mob1. We are not surprised that this reaction is less exothermic than the one for indane itself because we have lost the conjugation energy associated with conjugation of the endocyclic double bond attached to a benzene ring. 

Star polymers having several PS branches and only one poly(2-vinyl naphthalene), PVN branch were prepared by Takano et al. using anionic polymerization techniques [31]. Sequential anionic block copolymerization of (4-vinyl-phenyl) dimethylvinylsilane (VS) and VN was employed. The double bonds attached to silicon have to remain unaffected during the polymerization of VS. This was ac-... 

On the other hand, alkenyl aryllithiums can undergo diastereoselective cyclizations in very good yields. Pedrosa and coworkers163 reported that chiral 2-(o-bromophenyl)-substitutedperhydro-l,3-benzooxazines 281, initially transformed to the aryllithium derivative, gave the intramolecular 6-exo carbolithiation reaction with unactivated double bonds attached to the nitrogen substituent of the heterocycle (Scheme 87). By adding 2 equivalents of TMEDA to the aryllithium derivative 1,3-benzooxazines 281 prepared at —90 °C,... 

One concern that was raised by some scientists is the orientation of the interacting double bond in styrene with the silver surface. It was already shown that in ethylene, the double bond attaches parallel to the silver surface (49). More complicated substrates showed different interaction geometries and it is possible that the phenyl substitution may cause the C=C double bond to twist in a way that makes the interaction a bad model for ethylene (50,51). 

Generally, a C-C double bond attached to a cyclopropane ring reacts readily with chlorine and to give the corresponding vicinal... 

Dioxinones 27, with an endo double bond attached to a chiral auxiliary derived from (—)-men-thone, yield the corresponding adducts on addition to cyclopentadiene (9) with excellent diastereoselectivity 31. 

Soc. 1958, 222 Tanenbaum, Bassett, J. Biol Chem. 234, 1861 (1959). Has carcinogenic activity attributable to a.P-unsaturation together with an external conjugated double bond attached to 4 position of the y -lactone ring Dickens, Brit. Med Bull 20, 96 (1964). Review amd evaluation of studies of carcinogenic action in laboratory animals IARC Monographs 10,205-210 (1976). Also inhibits uptake of K+ ions in erythrocytes Kahn, J. Pharmacol Exp. Then 121, 234 (1957). Toxicity R. Kinostta, T. Shikata, "On Toxic... 

This double bond attachment is substantiated by carbon/hydrogen analysis before and after bonding. Furthermore, the basic high stability of the cyclodextrin bonded phases support the idea that a significant number of these types of double bond attachments are, in fact, present. In addition, it is not theoretically impossible that one cyclodextrin molecule could be anchored to the silica by three or more chains, although such attachment bonds have not been experimentally confirmed or identified. These types of phases have been used very successfully in the resolution of the enantiomers of a number of P- blockers (e.g. Propranolol, Atenolol,... 

Bloom and Shull deduced the generalization that microorganisms which can cause axial hydroxylation at a given carbon atom can also cause epoxidation of a double bond attached to the same carbon atom (B-66). The epoxide oxygen will have the same configuration as the hydroxyl group which is normally introduced at the saturated carbon atom. Their explanation of this thesis was that the pi electrons of the double... 

Cyclopolymerization is an intramolecular ring formation reaction. For example, as well as double bonds attached to the main chain [Equation (16-54a), rings in the main chain (Equations (16-54b) and (16-54c)] can also be formed in the polymerization of the acrylic anhydride, a 1-6 diene ... 

It was noticed in 1924 by the German chemist Julius Bredt (1855-1937) that one structural type was conspicuously absent among the myriad compounds isolated from sources in Nature. There seemed to be no double bonds attached to the bridgehead position in what are called bridged bicyclic molecules. The bridgehead position is the point at which the bridges meet (Fig. 3.44). Apparently, great... 

In allenes, the double bonds share a central carbon atom. There are other cumulated molecules in which heteroatoms (noncarbon atoms such as oxygen or nitrogen) take the place of one or more carbons of an allene and/or in which there are more than two double bonds in a row. When one end carbon of allene is replaced with an oxygen, the compound is called ketene (Fig. 12.6). If both end atoms are oxygens, the molecule is carbon dioxide. Cumulated hydrocarbons with three double bonds attached in a row are called cumulenes, although they can also be named as derivatives of 1,2,3-butatrienes (Fig. 12.6). Cumulenes are very reactive and most difficult to handle. 

FIGURE 14.6 Ball-and-stick models of ethene (a, c) and propene (b) Flexible springs are used to show a double bond. From the angle in (c) we can see that the geometry is planar around carbons where there is a double bond attached. Notice that the third carbon on propene (b) has the tetrahedral geometry, since it has only single bonds attached. 

It is tetrahedral when there is nothing but single bonds attached. It is trigonal planar when there is a double bond attached. It is linear when there is a triple bond attached. 

In the electron-dot formula of CO2, there are two electron groups (two double bonds) attached to the central atom. According to VSEPR theory, minimal repulsion occurs when two electron groups are on opposite sides of the central C atom. This gives the CO2 molecule a linear electron-group geometry and a linear shape with a bond angle of 180°. 

The basic and most important biologically active apocarotenoid in animal tissues is aU-trans-retinol also known as axeroftol or vitamin Aj (5-1). Retinol is an isoprenoid with 20 carbon atoms and five conjugated double bonds in the molecule, more precisely a diterpenic ahcychc alcohol with the so- called fl-ionone ring and a side chain of four conjugated double bonds attached to C-6. It is one of 16 possible stereoisomers. 

Stability and performance of AEM prepared using poly(4-vinyl pyridine-costyrene), quaternized with 1-bromooctane, and deposited on fibrous woven paper was unsatisfactory [189]. Sanchez and coauthors [190] discussed problems related to the use of certain AEMs. They pointed out that the so-called Hoffman degradation that involves attack of a hydroxyl on a-hydrogen in p-position to a quaternary ammonium attached to an aliphatic chain may cause its removal, followed by release of a tertiary amine and formation of a double bond at the end of a broken chain. Attachment of DABCO on short leash prevented chain break due to Hoffman degradation, but release of DABCO and generation of a double bond attached to the chain could take place. Perhaps thermal cross-linking by DABCO of poly(vinyl benzyl chloride) may solve this problem. Sulfonated polymers prepared by polymerization or copolymerization of phosphazene, siloxans, styrene, vinylidene fluoride, and various monomers with aromatic backbones, and possibly with aliphatic spacers, have been used. Various imides as well as PPS, PEK, PEEK, PSU, PEEKK, and PPSU can also be used [190,191]. 

In the oxidation of secondary alcohols, the products are ketones. Two hydrogen atoms are removed, one from the —OH group and another from the carbon bonded to the —OH group. The result is a ketone that has the carbon-oxygen double bond attached to alkyl groups on both sides. There is no further oxidation of a ketone because there are no hydrogen atoms attached to the carbonyl group. 

Under similar conditions, the pendant double bond attached to a 2,3-epoxy alcohol acts as an internal nucleophile attacking at C-3, resulting, after proton loss, in a mixture of cyclized products (eq 12). The cyclopropane-containing products are believed to arise via a retro-homo Prins reaction. Pendant triple bonds can also participate in related cyclization reactions and cyclic allenes result (eq 13). The observation that the threo isomer of the substrate shown in eq 12 is stable to Ti(0-/-Pr)4 has led to the suggestion that an intramolecular metal alkoxide is the active catalyst in successful cyclization reactions. 

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