Bond, acetylenic double

Ethylene has a carbon-carbon double bond acetylene has a carbon-carbon triple bond... 

One of the most important publications on this subject, considered frorn the chemical side, is that of Gertrude Woker. This investigator drew attention to the importance of multiple bonding. The double bond is often accompanied by a pleasant, but the triple or acetylenic linkage generally produces a disagreeable smell a multiplicity of double bond can produce an effect equivalent to a triple bond. 

Ethane, a component of natural gas, contains a C—C single bond. Ethylene, widely used to make plastics, contains a CDC double bond. Acetylene, used as fuel for welding torches, contains a CDC triple bond. 

Aliphatic- Straight- or branch-chain organic molecules that have saturated bonds (paraffins), double bonds (olefins), or triple bonds (acetylenes). 

Several vibrational modes in the excited singlet states of DPA have been identified from picosecond CARS measurements. The central C—C bond of DPA retains much of its triple-bond-like character in the S2 state however, the central C—C bond has double-bond-like character in the state. By analogy with the trans-bent form of S acetylene, it was proposed that S DPA has a trans-or cis-form bent structure that is consistent a previously proposed strucmre. It has been cautioned that, because of the conjugation between the phenyl groups and the central C—C bond, the S state may assume a structure different from the bent form. The interpretation of recent picosecond IR absorption measurements provide support for the trans-bent planar structure for S of DPA. The diphenylace-tylenic fluorophore has recently been incorporated into several chemosensor structures whose fluorescent signaling properties are controlled by the relative flexibilities of the molecules. ... 

Section 1.4 Many organic compounds have double or triple bonds to carbon. Four electrons are involved in a double bond six in a triple bond. H H =c H—c=c—H H H Ethylene has a carbon-carbon double bond acetylene has a carbon-carbon triple bond. 

They applied the same pseudopotential as before in the paper with title ab initio molecular calculations with pseudopotentials calculations of double-zeta quality on ethylene, acetylene, and water , but a linear combination of FSGO has been used in the following articles. A description of C-C bond for double and triple bond has been given in the pseudopotential-FSGO method. 

The C-H and C-C cr-bonds are all trigonal sp hybrids, with 120° bond angles. The two unhybridized p-orbitals form a 7r-bond, which gives the molecule its rigid planar structure. The two carbon atoms are connected by a double bond, consisting of one o and one tt. The third canonical form of 5/ -hybridization occurs in C-C triple bonds, for example, acetylene (ethyne). Here, two of the p AO s on each carbon remain unhybridized and can form two n -bonds, in addition to two (r-bonds. Acetylene H-C=C-H is a linear molecule, as shown below, since the p-hybrids are oriented 180° apart. 

Although acetylene adds four monovalent atoms while ethylene adds only two, it does not follow that the greater unsaturation is accompanied by a more rapid rate of addition. As a rule, the activity of the triple bond, measured by the rate of addition, is lower than the activity of the double bond. Acetylene forms explosive mixtures with air, and care should be exercised by the student to keep the generator away from all flames. 

The reactions of acetylene which have been mentioned are analogous to those of the unsaturated hydrocarbons containing a double bond. Acetylene and other compounds which contain a carbon atom in combination with hydrogen and joined to a second atom in the manner which is represented by a triple bond, that is, those containing the group H —C =, show characteristic properties which serve to distinguish them from other substances. Such compounds are converted into metallic derivatives when they are treated with an ammoniacal solution of cuprous chloride or of silver chloride. If acetylene is passed into a solution of cuprous chloride in ammonia, a red precipitate is formed which has the composition C2CU2. This compound, which is a carbide of copper, is usually called copper acetylide. It explodes, when dry, if it is struck or is heated to 100°-120°. When treated with hydrochloric acid or with a solution of potassium cyanide, acetylene is formed. 

Such structural formulas could be made more flexible if the existence of two bonds (a double bond) or three (a triple bond) between adjacent atoms were permitted. Thus, ethylene (C2H4), acetylene (C2H2), methyl cyanide (C2H3N), acetone (CsHeO), and acetic acid (C2H4O2) could be represented as follows ... 

In the cell-free preparation of the Dinophyta Amphidinium carterae, " C-labellled zeaxanthin 14 was incorporated into neoxanthin 18, and then into acetylenic diadinoxanthin 67 and C37 peridinin 72 (Fig. 106.3). In addition, the three carbon atoms (C-13, 14, 20 ) of peridinin were eliminated from neoxanthin (C-13,14,20) [57, 58]. In organic chemistry, the C-7,8 double bond of zeaxanthin can be oxidized to the triple bond (acetylene group) of diatoxanthin 65 [59]. Enzymes for these reactions remain unknown. 

Presumably this reaction proceeds by formation of the metal alcoholate, which undergoes nucleophilic addition to the acetylenic double bond. The resulting adduct then regenerates the alcoholate by proton exchange. Sodium and potassium hydroxides are the most common catalysts employed for this reaction. 

Dipolar cycloaddition reactions were investigated by Huisgen and his co-workers. 1, 3-Dipolar cycloadditions provide a versatile method for stereospecific synthesis of five membered heterocyclic compounds by the addition of 1 3-dipolar compoimds to ethylenic and acetylenic double bonds (dipolarfiles). 1, 3-dipolar systems are four n-electron species which undergo Kg+n g concerted cycloadditions across ic-bonds of olefins and acetylenes. 

Contact angles were measured on plasma polymers deposited from numerous hydrocarbon monomers of different structure containing triple bond, olefinic double bonds, aromatic and aliphatic structures. The results of contact angle measurements and evaluated surface energy properties for these polymers are summarized in Table II, column A. The data for plasma polymers from acetylene, ethylene, and hexane indicate that monomer unsaturation does not change substantially the dispersion component but increases the polar component to a considerable extent as in the case of acetylene. This, undoubtedly, is due to the high concentration of radicals in PP-AC and resulting rapid formation of carbonyls and... 

CH = C = CH— are called allenes after the simplest member of the series. They are said to have cumulated double bonds. They react in most cases normally, that is, each double bond is unaffected by the proximity of the other they are converted by heating into the isomeric acetylenes. Compounds of the type... 

The Diels-Alder Reaction consists in the direct combination of a compound containing a conjugated diene system u ith a reagent which possesses a double or triple bond activated bj suitable adjacent groups. Examples of such reagents are maleic anhydride, p-benzoquinone, acraldehyde and acetylene dicarboxylic esters. Combination always occurs at the 1,4 positions of the diene system ... 

Compounds containing a double or triple bond, usually activated by additional unsaturation (carbonyl, cyano, nitro, phenyl, etc.) In the ap position, add to the I 4-positions of a conjugated (buta-1 3-diene) system with the formation of a ax-membered ring. The ethylenic or acetylenic compound is known as the dieTwphile and the second reactant as the diene the product is the adduct. The addition is generally termed the Diels-Alder reaction or the diene synthesis. The product in the case of an ethylenic dienophile is a cyctohexene and in that of an acetylenic dienophile is a cyctohexa-1 4-diene. The active unsaturated portion of the dienophile, or that of the diene, or those in both, may be involved in rings the adduct is then polycyclic. 

Carbon can also form multiple bonds with other carbon atoms. This results in unsaturated hydrocarbons such as olefins (alkenes), containing a carbon-carbon double bond, or acetylenes (alkynes), containing a carbon-carbon triple bond. Dienes and polyenes contain two or more unsaturated bonds. 

The diol must have a cis double bond so we can use the acetylene trick again here. 

Synthesis The CO2H group spells trouble. We would certainly have to use an ester, but the a-bromoester is too reactive to use with an acetylene. Also there is a danger that the double bond in A will move into conjugation. We can get round all these problems with an epoxide and then oxidise at the end ... 

The addition of acetylides to oxiranes yields 3-alkyn-l-ols (F. Sondheimer, 1950 M.A. Adams, 1979 R.M. Carlson, 1974, 1975 K. Mori, 1976). The acetylene dianion and two a -synthons can also be used. 1,4-Diols with a carbon triple bond in between are formed from two carbonyl compounds (V. Jager, 1977, see p. 52). The triple bond can be either converted to a CIS- or frans-configurated double bond (M.A. Adams, 1979) or be hydrated to give a ketone (see pp. 52, 57, 131). 

Multiple bonds are very common m organic chemistry Ethylene (C2H4) contains a carbon-carbon double bond m its most stable Lewis structure and each carbon has a completed octet The most stable Lewis structure for acetylene (C2H2) contains a carbon-carbon triple bond Here again the octet rule is satisfied... 

Hydrocarbons that contain a carbon-carbon triple bond are called alkynes Non cyclic alkynes have the molecular formula C H2 -2 Acetylene (HC=CH) is the simplest alkyne We call compounds that have their triple bond at the end of a carbon chain (RC=CH) monosubstituted or terminal alkynes Disubstituted alkynes (RC=CR ) have internal triple bonds You will see m this chapter that a carbon-carbon triple bond is a functional group reacting with many of the same reagents that react with the double bonds of alkenes... 

Unlike ethynylation, in which acetylene adds across a carbonyl group and the triple bond is retained, in vinylation a labile hydrogen compound adds to acetylene, forming a double bond. 

When aiomatics aie present, they can capture the intermediate vinyl cation to give P-aryl-a,P-unsatutated ketones (182). Thus acylation of alkyl or aryl acetylenes with acyhum salts in the presence of aromatics gives a,P-unsaturated ketones with a trisubstituted double bond. The mild reaction conditions employed do not cause direct acylation of aromatics. 

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