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List of Chemical Substances
Published in T.S.S. Dikshith, and Safety, 2016
Allene is colorless with a sweet odor. It is a flammable gas and may cause flash fire at room temperature. Allene is the simplest member of the 1,2-diene class of compounds of hydrocarbons of the aliphatic chemical family. It is a benzene and petroleum ether. Allenes are not as stable as conjugated dienes or isolated dienes. Allene is slightly more strained than the isomeric methylactylene. Allene is chiefly used in organic synthesis. It is incompatible with metals and oxidizing materials, therefore it is important to avoid copper and silver and their alloys when used under high pressure or temperature.
Organometallic Compounds as Heterogeneous Catalysts
Published in Varun Rawat, Anirban Das, Chandra Mohan Srivastava, Heterogeneous Catalysis in Organic Transformations, 2022
Garima Sachdeva, Monu Verma, Varun Rawat, Ved Prakash Verma, Manish Srivastava, Sudesh Kumar, Singh Vanshika
Allenes are the organic compounds in which one carbon atom has double bonds with the two adjacent carbon centers. They are categorized as cumulative dienes. Varghese and the group had described the method for synthesizing substituted allenes that are further used to synthesize chiral compounds. Carbocupration of alkynyl sulfoxide, followed by homologation of vinyl copper with zinc carbenoid, lead to the formation of allyl zinc derivative that further undergoes β-elimination to form substituted allene (Figure 4.27) [52].
Highly delocalised molecular orbitals in boron-, carbon- and nitrogen-based linear chains: a DFT study
Published in Molecular Physics, 2022
AbhayRam Balakrishnan, S. Vijayakumar
BnH4 chains showed varying molecular orbitals with chain length, possibly resulting from their variations in ground-state structures. Helical molecular orbitals were noted for some values of n. While for n = 6, and n = 10 HOMO and LUMO are helical, for n = 2, LUMO orbital alone is helical. Previously helical orbitals were only reported in LCC [7,35–38], and this is the first time non-carbon chains have helical orbitals.Only chains with the odd number of carbon atoms show helical orbitals starting from allene in cumulenes. The helical orbitals of boron chains show a modified helicity compared to cumulenes chains, as shown in Figure 7. While the 2n + 1 cases for CnH4 showed helical orbitals for n = 1,2,3 … , the 4n + 2 cases of BnH4 chains are helical.
4,5,9,10-Tetrahydrocycloocta[1,2-c; 5,8-c′]dithiophene from bis(2-chloropropen-3-yl)sulfide: spectral and theoretical monitoring of the formation
Published in Journal of Sulfur Chemistry, 2021
Vladimir I. Smirnov, Lidiya M. Sinegovskaya, Vladimir A. Shagun, Valentina S. Nikonova, Nikolai A. Korchevin, Igor B. Rozentsveig
Allene and its alkyl derivatives are known to absorb in the region of 230–260 nm [19,20]. For instance, in the UV spectrum of methylallylene, the absorption bands are observed at 258 and 225 nm, which are attributed to partially allowed (due to electron-vibration interactions) - and transitions in the allene fragment [21]. The bands with an optical density of 0.38 and 0.41 are assigned to these transitions (Figure 1(a), curves 2, 3). The interaction of Cβ-carbon atoms of the allene fragments results in intramolecular cyclodimerization.
Ab initio molecular dynamics study of the reactions of allene cation induced by intense 7 micron laser pulses
Published in Molecular Physics, 2019
Yi-Jung Tu, H. Bernhard Schlegel
The PES for the isomerisation and fragmentation of allene cation (H2C=C=CH2+) has been studied previously by Mebel and Bandrauk using the CCSD(T) calculations [9]. In the present work, the energetics of allene cation PES are calculated at the B3LYP/6-31 + G(d,p) level of theory and summarised in Figure 1. As shown in the previous study by Mebel and Bandrauk, there are four stable C3H4+ structures: allene cation (1), vinylmethylene cation (2), propyne cation (3), and cyclopropene cation (4). The most stable C3H4+ structure is allene cation (1) with a calculated dihedral angle of 49.6 degrees between the two CH2 planes. A 1,2 hydrogen migration in allene cation leads to the formation of vinylmethylene cation (2), which is 25.5 kcal/mol higher than allene cation. The transition state for 1,2 hydrogen migration has a planar geometry and is 31.3 kcal/mol above allene cation. Vinylmethylene cation can undergo cyclisation with a very small energy barrier of 2.2 kcal/mol to form cyclopropene cation (4, which is 24.1 kcal/mol higher than allene cation) or return to allene cation with a small barrier of 5.8 kcal/mol. The 1,3 migration of hydrogen in allene cation has an energy barrier of 40.6 kcal/mol for the formation of propyne cation (3), which is 16 kcal/mol higher than the allene cation. The transition state for 1,3 hydrogen migration has a nonplanar geometry where the hydrogen moving above the middle carbon is perpendicular to the H2C=C=CH+ plane. Propyne cation can also be converted to cyclopropene cation, but this step has a high energy barrier of 58.9 kcal/mol. In addition to isomerisation, there are three dissociation channels: loss of hydrogen to form H2CCCH+ (5, 72.6 kcal/mol higher than 1), loss of hydrogen from cyclopropene cation to form c-C3H3+ (6, 23.6 kcal/mol higher than 4), and loss of H2 from propyne cation to produce HCCCH+ (7, 52.7 kcal/mol higher than 3). The relative energies of isomers and transition states calculated using B3LYP/6-31 + G(d,p) are 3–7 kcal/mol higher than the CCSD(T) calculations of Mebel and Bandrauk, but this is acceptable for the ab initio MD simulations in this study.