Conjugation double or triple bonds

It is often of importance to detect compounds in the chromatogram without cauang chemical change. In the case of substances containing conjugated double or triple bonds observation under UV light is to be reconunended (Sec. 2.2.2). If... 

The carboxyl group in aliphatic FA is a poor chrom-atophore with absorption maximum 210nm in ethanol, with e = 50. The UV absorption properties improve with the presence of unsaturated bonds especially in the case of conjugated double or triple bonds. 

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. 

The Diels-Alder reaction,is a cycloaddition reaction of a conjugated diene with a double or triple bond (the dienophile) it is one of the most important reactions in organic chemistry. For instance an electron-rich diene 1 reacts with an electron-poor dienophile 2 (e.g. an alkene bearing an electron-withdrawing substituent Z) to yield the unsaturated six-membered ring product 3. An illustrative example is the reaction of butadiene 1 with maleic anhydride 4 ... 

Reduction of The Double or Triple Bonds of Conjugated Systems... 

A second important reaction type considered in this chapter is conjugate addition, which involves addition of nucleophiles to electrophilic double or triple bonds. A crucial requirement for this reaction is an electron-withdrawing group (EWG) that can stabilize the negative charge on the intermediate. We focus on reactions between enolates and a,(3-unsaturated carbonyl compounds and other electrophilic alkenes such as nitroalkenes. 

When the C=S bond is conjugated with double or triple bonds, thioketones can also behave as heterodienes93 104 towards dienophiles. If thioketone contains an aromatic ring, the [4+2] cycloaddition can be followed by 1,3-protot-ropy to restore the ring aromaticity,105 108 forming lH-2-benzothiopyrans as shown in Scheme 13, where 4,4 dimethoxythiobenzophenone reacts with the dienophile dimethyl acetylenedicarboxylate (DMAD).105... 

When C=Se is conjugated with double or triple bonds, selenoketone can also behave as a heterodiene in the presence of the dienophiles. A-selenoacylami-dines, used as l-selena-3-aza-l,3-dienes with 1,5 equivalents of the dienophile DMAD are converted229,231 to 4H-l,3-selenazines, Scheme 28, with 10 equivalents being transformed into tetrasubstituted 4H-selenopyran derivatives (Scheme 31). 

Diels-Alder reaction org chem The 1,4 addition of a conjugated diolefin to a compound, known as a dienophile, containing a double or triple bond the dienophile may be activated by conjugation with a second double bond or with an electron acceptor. jdelz jal-dar re,ak-shan ... 

Acetylides ROOM having a double or triple bond in conjugation with the terminal triple bond are more soluble in NH3 or organic solvents than acetylides, in which this conjugation is absent. 

The reaction is very general. The aldehyde or ketone may be aliphatic, alicyclic, or aromatic (including diaryl ketones) it may contain double or triple bonds it may contain various functional groups, such as OH, OR, NR2, aromatic nitro or halo, acetal, or even ester groups.643 Double or triple bonds conjugated with the carbonyl also do not interfere, the attack being at the 0=0 carbon. 

In benzaldehyde and many other similar molecules, on the other hand, the resonance effect directs toward the meta positions, this resulting whenever the substituted group R contains an electronegative atom and a double or triple bond conjugated with the benzene ring (R = COOH, CHO, NO, COCHa, SOaH, CN, etc.). The structures leading to this effect, F, G, and H, are of the types... 

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