Diacetylene

Diacetylene (1,3-butadiyne) is the first member of the polyyne series with conjugated triple bonds. It is the simplest compound with a single bond between two sp-hybridized carbon atoms and is a suitable model for the study of the influence of conjugation effects on ground-and excited-state properties. Diacetylene has been the subject of numerous theoretical investigations which are discussed briefly in this section. 

The peculiar character of this single bond has been demonstrated by calculating the reaction energy for the isodesmic transformation, HCsC—CsCH + 2 C2H2 + C2H5 the 

In a study on the proton afrinity of diacetylene, Botschwina et al. reported more extended ab-initio calculations for C4H2 by allowing for effects of electron correlation, using the coupled-electron-pair approximation (CEPA) [207], Thor obtained C —C bond lengths of 

I Modern Computational and Theoretical Aspects of Acetylene Chemistry 

2114 and 1.3802 A, respectively. The proton affinity of C4H2 was calculated to be 177.3 kcal/mol. In an earlier study, Deakyne et al. determined the proton affinity of diacetylene by ion cyclotron resonance bracketing experiments as 180 1 kcal/mol (133). From SCF, MP2, and MP3 calculations with the 6-31G basis set, they obtained values of 189.9, 179.9 and 185.8 kcal/mol, respectively. 

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Photopolymerization reactions of monolayers have become of interest (note Chapter XV). Lando and co-workers have studied the UV polymerization of 16-heptadecenoic acid [311] and vinyl stearate [312] monolayers. Particularly interesting is the UV polymerization of long-chain diacetylenes. As illustrated in Fig. IV-30, a zipperlike process can occur if the molecular orientation in the film is just right (e.g., polymerization does not occur readily in the neat liquid) (see Refs. 313-315). 

Chemical properties of deposited monolayers have been studied in various ways. The degree of ionization of a substituted coumarin film deposited on quartz was determined as a function of the pH of a solution in contact with the film, from which comparison with Gouy-Chapman theory (see Section V-2) could be made [151]. Several studies have been made of the UV-induced polymerization of monolayers (as well as of multilayers) of diacetylene amphiphiles (see Refs. 168, 169). Excitation energy transfer has been observed in a mixed monolayer of donor and acceptor molecules in stearic acid [170]. Electrical properties have been of interest, particularly the possibility that a suitably asymmetric film might be a unidirectional conductor, that is, a rectifier (see Refs. 171, 172). Optical properties of interest include the ability to make planar optical waveguides of thick LB films [173, 174]. 

Similar systems to those mentioned above exist where the constituent monomer contains the diacetylene group. 

A summary of the studies perfonned on symmetrical compounds having a diacetylene group at the centre is given in [94]. Most of the materials studied in the context of LB films have been diyonic acids (figure C2.4.8). 

Figure C2.4.8 Diacetylene stmcture employed to prepare polymeric LB films (a) and principle in diacetylene polymerization (b).

If these materials are deposited as LB multilayers, polymerization can be induced either by thennal or optical means. This subject has been intensively studied [95, 96, 92, 98 and 99]- Since parameters such as m, subphase components, pH and polymerization before and after dipping, as well as temperature and wavelength employed for polymerization can be varied, the literature on diacetylenes is extensive and the reader is referred for example to the book of Tredgold [1001. 

Tieke B, Graf H J, Wegner G, Naegele D, Ringsdorf H, Baner]ie A, Day D and Lando J B 1977 Polymerization of mono- and multilayers forming diacetylenes Coiioid Poimer Soi. 255 512-31... 

If undiluted diacetylene is required, the experiment can be carried out in the same way, but preferably on a smaller scale. 3 Traps should then be used and the stream of nitrogen should be slower. The boiling point of diacetylene is said to be about 10°C. The solutions of diacetylene probably can be stored (under nitrogen in the refrigerator) for at least 24 h without decomposition. Though explosions have never been experienced by the authors, it is advisable to handle diacetylene with the necessary respect. 

Diacetylene (HC=C—C=CH) has been identified as a component of the hydrocarbon rich atmospheres of Uranus Neptune and Pluto It is also present m the atmospheres of Titan and Triton satellites of Saturn and Neptune respectively... 

It is also possible for a single monomer to behave as both diene and dienophile. Heating diacetylene [XXII] produces an infusible material which may be rationalized as follows ... 

Squalane [111-01-3] (fully saturated squalene) is produced synthetically by the coupling of two molecules of geranyl acetone with diacetylene, followed by dehydration and complete hydrogenation (205). Squalane can also be made by dimerization of dehydroneroHdol, followed by dehydrogenation and hydrogenation (206). 

LB films of CO-tricosenoic acid, CH2=CH—(CH2)2qCOOH, have been studied as electron photoresists (26—28). A resolution better than 50 nm could be achieved. Diacetylenic fatty acids have been polymerized to yield the corresponding poly (diacetylene) derivatives that have interesting third-order nonlinear optical properties (29). 

LB Films of Polymerizable Amphiphiles. Stxidies of LB films of polymerizable amphiphiles include simple olefinic amphiphiles, conjugated double bonds, dienes, and diacetylenes (4). In general, a monomeric ampbipbile can be spread and polymerization can be induced either at tbe air—water interface or after transfer to a soHd substrate. Tbe former polymerization results in a rigid layer tbat is difficult to transfer. 

Molecular films are of intense current concern in electronics. For instance, diacetylenes and other polymerisable monomer molecules have been incorporated into L-B films and then illuminated through a mask in such a way that the illuminated areas become polymerised, while the rest of the molecules can be dissolved away. This is one way of making a resistance for microcircuitry. L-B films have also found a major role in the making of gas-sensors (Section 11.3.3). 

A solution of the monosodium salt of diacetylene in 300 ml of liquid ammonia is prepared from 13.8 g (0.6 g-atoms) sodium and 24.6 g (0.2 moles) l,4-dichlorobut-2-yne. To this mixture is added a suspension of 5 g (17.6 mmoles) 3-methoxyestra-l,3,5(10)-trien-17-one in anhydrous tetrahydrofuran at —40° and the reaction mixture is stirred and maintained at this temperature for 2 hr. Ammonium chloride is then added and the ammonia is allowed to evaporate overnight. The residual solids are extracted with methylene dichloride and the extracts washed with water, dried over magnesium sulfate, and evaporated at 70°. The resultant dark gum is... 

The first representative of the acetylenic derivatives, 3(5)-ethynylpyrazole, was obtained by condensation of diacetylene with diazomethane by Kuhn and Henkel (41LA279) and later by other authors (69IZV2546), and by reaction of acetylene with diazopropyne (62AG252 68LA113) (Scheme 2). 

The composition of the mixture of products of different structures depends on the diacetylene diazomethane ratio (68LA124). With a 1 1 ratio of butadiyne and diazomethane, 3(5)-ethynylpyrazole dominates (55%). The yields of isomeric 3- and 5-ethynyl-l-methylpyrazoles are 8 and 11%, respectively. The double excess of diazomethane leads mainly to a mixture of N-methylated isomers (81%), 10% of 3(5)-ethynylpyrazole, and a small amount (3%) of bipyrazole (68LA124) (Scheme 3). 

The monosubstituted diacetylenes, including the 3-triethylstannyl derivative (81%) (71ZOB2230), react with the 1,3-dipole to yield a 3(5)-alkyn-l-ylpyrazole (65ZOR610 68KGS695) (Scheme 4). 

According to publications (68LA113 71CAS1731 72BSF4781), disubstituted diacetylenes react with diazomethane to form both 3- and 4-acetylenyl-substituted... 

The standard technique for obtaining alkynylpyrazoles consists of mixing up the ether solutions of diazoalkane and diacetylene or its derivatives (or diazopropyne and acetylene) and keeping the reaction mixture either for several hours or for three weeks within a narrow temperature range (0-20°C) (Tables II and III). 

Under similar conditions, the interaction between diacetylene and diazoethane (68CB3700) gives rise to 5-ethynyl-3-methyl-l//-pyrazole in 34% yield (Scheme 11). 

Thus, the reaction of diazoalkanes andnitrilimines with diacetylenic derivatives can be used as a method for synthesizing acetylenylpyrazoles. 

Another type of cyclization leading to acetylenylpyrazoles is the interaction between a-acetylenic and -diacetylenic ketones and nitrogen-containing binucleophiles. 

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