Triple bond position

The results for the complete series of acetylenic acids, except A3a, are given in Figure 5 by a plot of the area under the curve vs. triple bond position (see Figure 4 for some of the 7t-A curves). All of the compounds form more expanded films than the corresponding ethylenic acids consequently, the range of areas used for the comparisons in Figure 5 was chosen arbitrarily as 140 to 50 A2/molecule. Here, the pattern of change is quite different from that with the ethylenic series. The A2a and A4a are relatively condensed and similar to each other. 

PED. The triple-bond positional isomers of PED, lO-(l-propynyl) estr-4-ene-3,17-dione, and the 10-ethynyl, 10-cyano and 1-methyl cyanide analogs were not suicide inhibi-torsi2l,l3l,l32 10-[[li ]-l-hydroxy-2-propynyl], 10-[[lS]-l-hydroxy-2-propynyl] and 10-(l-oxo-2-propynyl) estr-4-ene-3,17-dione were prepared as potential PED metabolites (Scheme 16) and tested for their aromatase inhibitory activity on human placental enzyme. While the [Ii ]-hydroxy isomer was the only competitive inhibitor of aromatase, the other two oxidized analogs, [I S]-hydroxy and 1-oxo-derivatives, had very weak inhibitory properties compared to PED (Ki 27 jjM and 12 juM vs 23 nM for PED and ty/, of 4 min and 2.16 min vs 10.4 min for PED) . These observations were in contrast to the a priori assumption that 10-(l-oxo-2-propynyl)estr-4-ene-3,17-dione might be the most active derivative in the series, due to its Michael acceptor structure i8,121 similarly, the 19-hydroxylated propargyl derivatives of 3-deoxyandrost-4-ene-17-one and androst-4-ene-3,6,17-trione were very weak mechanism-based inhibitors of aromatase ". ... 

The naming protocol for alkynes is similar to that used for alkenes. As with the double bond of alkenes, the triple bond position is designated by assigning it a number, which is kept as low as possible. When both double and triple bonds are present, the compounds are named as enynes, and the numbers designating the positions of the multiple bonds kept as low as possible. If the numbering scheme could produce two names in which the lower number could go to either the -ene or the -yne, the -ene gets it (Fig. 3.59). 

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 ... 

The position of the triple bond is established by oxidation of the latter by means of alkaline potassium permanganate solution to sebacic acid, H02C(CH2)gC0jH, m.p. 133°. 

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 last isomerization is remarkable in that the triple bond can shift through a long carbon chain to the terminus, where it is fixed as the (kinetically) stable acetylide. The reagent is a solution of potassium diami no-propyl amide in 1,3-di-aminopropane. In some cases alkali metal amides in liquid ammonia car also bring about "contra-thermodynamic" isomerizations the reactions are successful only if the triple bond is in the 2-position. 

In naming alkynes the usual lUPAC rules for hydrocarbons are followed and the suffix ane is replaced by yne Both acetylene and ethyne are acceptable lUPAC names for HC=CH The position of the triple bond along the chain is specified by number m a manner analogous to alkene nomenclature... 

Univalent radicals have the endings -enyl, -ynyl, -dienyl, -diynyl, etc. When necessary, the positions of the double and triple bonds are indicated by locants, with the carbon atom with the free valence numbered as 1. Examples ... 

Bivalent radicals derived from unbranched alkenes, alkadienes, and alkynes by removing a hydrogen atom from each of the terminal carbon atoms are named by replacing the endings -ene, -diene, and -yne by -enylene, -dienylene, and -ynylene, respectively. Positions of double and triple bonds are indicated by numbers when necessary. The name vinylene instead of ethenylene is retained for —CH=CH—. 

The formation of acyl halide-Lewis acid complexes have been observed by several methods. For example, both 1 1 and 1 2 complexes of acetyl chloride, with AICI3 can be observed by NMR spectroscopy. The existence of acylium ions has been demonstrated by X-ray diffraction studies on crystalline salts. For example, crystal structure determinations have been reported for /i-methylphenylacylium and acetylium ions as SbFg salts. There is also a good deal of evidence from NMR measurements which demonstrates that acylium ions can exist in nonnucleophilic solvents. " The positive charge on acylium ions is delocalized onto the oxygen atom. This delocalization is demonstrated in particular by the short O—C bond lengths in acylium ions, which imply a major contribution from the structure having a triple bond ... 

Carbon has six electrons around the atomic core as shown in Fig. 2. Among them two electrons are in the K-shell being the closest position from the centre of atom, and the residual four electrons in the L-shell. TTie former is the Is state and the latter are divided into two states, 2s and 2p. The chemical bonding between neighbouring carbon atoms is undertaken by the L-shell electrons. Three types of chemical bonds in carbon are single bond contributed from one 2s electron and three 2p electrons to be cited as sp bonding, double bond as sp and triple bond as sp from the hybridised atomic-orbital model. 

Hydrogenation of alkynes to alkenes using the Lindlai catalyst is attractive because it sidesteps the regioselectivity and stereoselectivity issues that accompany the dehydration of alcohols and dehydrohalogenation of alkyl halides. In tenns of regioselectivity, the position of the double bond is never in doubt—it appears in the carbon chain at exactly the sane place where the triple bond was. In tenns of stereoselectivity, only the cis alkene forms. Recall that dehydration and dehydrohalogenation normally give a cis-trans mixture in which the cis isomer is the minor product. 

The most important members of this class are the osmium nitrido, and the osmyl complexes. The reddish-purple K2[OsNCl5] mentioned above is the result of reducing the osmiamate. The anion has a distorted octahedral structure with a formal triple bond Os=N (161pm) and a pronounced /ram-influence (pp. 1163-4), i.e. the Os-Cl distance trans to Os-N is much longer than the Os-Cl distances cis to Os-N (261 and 236 pm respectively). The anion [OsNCls] also shows a rram-effect in that the Cl opposite the N is more labile than the others, leading, for instance, to the formation of [Os NCl4] , which has a square-pyramidal structure with the N occupying the apical position. 

All five models for ethane show roughly the same information. The Wire model looks like a line formula in your chemistry textbook, except that all atoms, not just earbons, are found at the end of a line or at the intersection of lines. (The only exception occurs where three atoms lie on a line. Here, a Wire model will not show the exact position of the center atom.) The Wire model uses color to distinguish different atoms, and one, two and three lines to indicate single, double and triple bonds, respectively. 

The first step in the addition of an electrophile such as HBr to an alkyne involves protonation and subsequent formation of an intermediate vinyl cation. Where does propyne protonate Compare energies of 1-methylvinyl and 2-methylvinyl cations. Which is more stable Why Measure CC bond distance in the more stable cation. Does the cation incorporate a full triple bond (as in propyne) or a double bond (as in propene). Examine atomic charges and electrostatic potential maps to locate the positive charge in the two cations. Is the more stable ion the one in which the charge is better delocalized Use the charges together with information about the ions geometry to draw Lewis structures (or a series of Lewis structures) for 1-methylvinyl and 2-methylvinyl cations. 

Arynes are intermediates in certain reactions of aromatic compounds, especially in some nucleophilic substitution reactions. They are generated by abstraction of atoms or atomic groups from adjacent positions in the nucleus and react as strong electrophiles and as dienophiles in fast addition reactions. An example of a reaction occurring via an aryne is the amination of o-chlorotoluene (1) with potassium amide in liquid ammonia. According to the mechanism given, the intermediate 3-methylbenzyne (2) is first formed and subsequent addition of ammonia to the triple bond yields o-amino-toluene (3) and m-aminotoluene (4). It was found that partial rearrangement of the ortho to the meta isomer actually occurs. 

IV-Methylpyrrole with (Cp IrH3)2 and 3,3-dimethyl-1-butene gives a couple of unique organometallic products, 86 and 87 (990M134). In 86, the C—H bond in position 2 is activated and a rare tiVC) ti (C=C) coordination mode is realized. Species 87 is a zwitterionic compound containing a triple bond between the iridium atoms. 

It was assumed that the failure of cyclization of 3-amino- and 5-amino-4-acetylenylpyrazole derivatives is due both to the decreased nucleophilicity of the amino groups in the acceptor positions 3 and 5 of the pyrazole ring and to the low electrophilicity of the triple bond carbons in position 4 of the ring. 

Moreover, when carbamino and nitro groups are simultaneously in the ortho position to the triple bond, isomerization occurs only with participation of the amide group (Scheme 125). 

Nevertheless, the adjacent position of the amide and acetylenic groups was used in another type of heterocyclization. The nitrogen atom in the amide group is a weak nucleophile. Therefore, the N anion should be generated by potassium ethoxide. There are two possible variants of nucleophilic addition to the triple bond. Only one takes place, i.e., the formation of y-lactam. After 7 h of heating in EtOH in the presence of KOH, amide 72 isomerized into the known isoindoline 73 in 80% yield (Scheme 128). 

Intramolecular addition of the amide group to the triple bond in pyrazoles is more difficult, and results in closure of the 5-lactam rather than the y-lactam ring. The reaction time of the 4-phenylethynylpyrazole-3-carboxylic acid amide under the same conditions is extended to 42 h (Scheme 129) (Table XXVII). The cyclization of l-methyl-4-phenylethynyl-l//-pyrazole-3-carboxylic acid amide, in which the acetylene substituent is located in the 7r-electron-rich position of the heterocycle, is the only one complete after 107 h (Scheme 130) (90IZV2089). 

In general, it is diffieult to prediet the outeome of eyelizations of alkynylpyrazole diazonium salts, even with elosely related arrangements of funetional groups, sinee reaetion ean oeeur at both the a- and /3-earbon atoms of the aeetylenie substituent. Moreover, it is known that the eleetrophilieity of the diazo group and the nueleophilieity of a triple bond markedly depend on their positions in the pyrazole ring and that this ean affeet both the eourse and ease of eyelization and even its viability (83IZV688). 

Indeed, in the speetrum of ethynylpyrazole 94, the triple bond appears at 2112 em and then in the speetrum of earbinol 95, as in other disubstituted aeetylenes, their frequeney inereases by about 100 em . Note that the high intensity of the 2112 em band of eompound 94 is likely to result from the elevated eleetron density at position 4 of the pyrazole ring and the resulting inerease in the dipole moment of the triple bond eonjugate to it. 

Alkyne nomenclature follows the general rules for hydrocarbons discussed in Sections 3.4 and 6.3. The suffix -yne is used, and the position of the triple bond is indicated by giving the number of the first alkyne carbon in the... 

In all the preceding cases, the double or triple bond of the dienophile is next to the positively polarized carbon of an electron-withdrawing substituent. Electrostatic potential maps show that the double-bond carbons are less negative in these substances than in ethylene (Figure 14.8). 

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