C5 C7 and

For C7, Slanina et al. located a cyclic C2V symmetrical minimum structure using MP2/6-31 methodology and found it only 2.2 kcal/mol higher in energy than the linear form [254]. However, an MP4 treatment at the MP2/6-31G geometries increases the separation to about 17.5 kcal/mol. Another cyclic C2V symmetrical isomer was calculated to be 1.12 eV 

I Modern Computational and Theoretical Aspects of Acetylene Chemistry 

Two recent ab-initio studies are devoted to the determination of the ground-state structure of Cg. Parasuk and AlmlOf concluded that the cyclic polyacetylenic structure ( Ag) and the linear cumulenic g state are essentially isoenergetic [260]. However, the choice of basis sets and methods (MRCI modified coupled-pair functional, MCPF) heavily affects the difference in energy between the linear and cyclic forms of Cg, and so the results are quite uncertain. On the other hand, Slanina et al. proposed a nonplanar Z)2d symmetrical cyclic structure as the minimum-energy structure of Cg [261]. According to their MP2/6-31G calculations, this form is 13 kcal/mol lower in energy than the planar Qa structure. Unexpectedly, all the C-C bond lengths in the species are equivalent (1.339 A). DFT calculations favor the linear structure as compared with a planar cyclic one, but nonplanar species seem to have not been considered in this study [236]. 

CISD calculations (DZP basis set) for several cyclic and linear isomers of Cio (see Fig. 1-10, 8-12) were performed by Liang and Schaefer [262]. They concluded that (i) the monocyclic forms of Cio are considerably more stable than the linear structures (ii) the 0, symmetrical cumulenic structure 9 is the ground state, but electron correlation decreases the energy difference between 9 and the alternative ring structures 8 and 10 and (iii) the linear acetylenic structure 12 is just slightly less stable than the linear cumulene 11. 

Another sophisticated investigation into the nature of monocyclic Cjo, using coupled cluster methodology, was presented by Watts and Bartlett [263]. Structure 9 was found to be a local minimum, while the fully symmetrical structure 8 shows one imaginary frequency and 

---

The diethylaluminum chloride was also a catalyst for the polymerization of ethylene. Very similar products were obtained in parallel polymerizations carried out at 300° with diethylaluminum chloride and with a mixture of aluminum chloride and aluminum. The distillation curves showed marked plateaus for C6, Cs, and Cj0 hydrocarbons with complete absence of C5, C7 and C9. The bromine numbers indicated that these fractions were mixtures of paraffins and olefins. 

Zeolite Beta has also been studied for isobutane/butene alkylation (65, 66), but it was less selective to the desired TMP than USY, suggesting some diffusional limitations for these highly branched products at the relatively low reaction temperatures used. In fact, an increase of activity was observed when decreasing the crystal size of the Beta zeolite (66). As for USY zeolites, the activity, selectivity and deactivation rate of Beta zeolite were influenced by the presence of EFAL species (67). Medium pore zeolites, such as ZSM-5 and ZSM-11 were also found active for alkylation, but at temperatures above 100°C (68, 69). Moreover, the product obtained on ZSM-5 and ZSM-11 contained more light compounds (C5-C7), and the Os fraction was almost free of trimethylpentanes, indicating serious pore restrictions for the formation of the desired alkylation products. 

Not only are products with carbon numbers that are multiples of four are formed, but so also are C5-C7 and C9, Cio, and higher hydrocarbons. Cracking is invariably associated with oligomerization. The heavy cations formed by oligomerization have a tendency to fragment, forming C4-C16 cations and alkenes, according to the (3-scission mle, as depicted schematically in Reaction... 

Among the oils that contain carbon-carbon double bonds as the functional groups, linseed, tung, corn, cottonseed, rapeseed, and soybean are more widely used as polymeric sources. Linseed oil is extracted from the seeds of the flax plant Linum usitatissimum). The major constituents of linseed oil are a-linolenic acid (60%), linoleic acid (29%), and oleic acid (27%). This composition varies with changes in climatic conditions. On the other hand, tung oil, also called china wood oil, is derived from the seeds or nuts of the trees aleurites fordii and A. montana. The major constituent of tung oil is eleostearic acid (77-82%), whereas the other important components of tung oil are oleic acid (3.5-12.7%) and linoleic acid (8-10%). It is known that the carbon-carbon double bond in oleic acid is at C9, in linoleic acid it is at C6 and C9, and in linolenic acid it is at C3, C6, and C9, whereas eleostearic acid has double bonds at positions C5, C7, and C9. 

For purposes of this section, the chemical-specific parameters for the petroleum hydrocarbon fractions are based on selecting a midpoint for the fraction, based on empirical data unified by equivalent carbon number (EC). The fractions labeled as C5-C7 and >C7-C8 are characterized by one compound only, benzene and toluene, respectively. Remaining fractions are characterized by multiple compounds, as described in TPHCWG (1997b). Representative physical parameters for TPH fractions are presented in Table 5-7. 

Table 12.6 C5-C7 and Cg product distribution during initial alkylation stage [13],...

At sufficiently high I/O, selectivity vas optimized by varying reaction temperature. When the temperature vas lo vered, less C5-C7 and more of the desired Cg compounds vere formed. Also, at lo ver temperature, isomerization of high-octane TMPs to low-octane DMHs was reduced. However, when the temperature was reduced too much at a given olefin space velocity, overall olefin conversion was... 

The addition of about 25% isobutene on olefins resulted in a loss of less than 0.5 RON. This loss may be attributed to a somewhat higher formation level of C5-C7 and Cg + compounds. For H2SO4 alkylation, the same amount of feed isobutene would lead to a loss of about 1 RON. 

Another plant licensed by H. Koch to Enjay Chemical Co. in Baton Rouge, USA, came onstream in 1965. This plant is designed to make the so-called Neo-acids (branched C5-, C7- and CjQ-acids) with a capacity of 4500 tons per year. As catalyst BF3/2H2O is used [796, 1002]. 

Phthalates (esters of phthalic acid, also called 1,2-benzenedicarboxylic acid) DOP (DEHP), dioctyl phthalate (di-2-ethylhexyl phthalate) DUP, diun-decyl phthalate DINP, diisononyl phthalate DIDP, diisodecyl phthalate 6-lOP, mixture of C5, C7, and C9 straight-chain phthalates 71 IP, mixture of C6, C8, and CIO linear and branched-chain phthalates 9-1 IP, mixture of C8, C9, and CIO linear and... 

Furthermore, significant chemical shift differences between a- and p-anomers are observed for C4 and C6 as a result of 1,3-diaxial interactions between the protons in these positions and the anomeric centre (Bhattacharjee et al. 1975). The resonance positions of C2, C3, C5, C7, and C9 show only minor differences between a- and p>anomers, whereas Cl and C8 occupy intermediate positions in this respect. The i C resonances for pNeuSAc and pNeuSGc in aqueous solutions are compiled in Table 11. Hydroxylation of the CH3 group of the N-acetyl substituent results in two alterations in the i C-NMR spectrum a strong downfield shift for the resonance of the involved carbon and a small downfield shift for the neighbouring carbonyl carbon. 

Therefore, these reactions may be used for quantitative measurements, for example by volumetric or gravimetric techniques (Topics C5, C7 and C8). 

---