Alkyl alkanoates

Insertion of carboxy groups between C2 and C3 of the molecules in mixtures of even shorter n-alkanes, hexadecane and octadecane, does allow a new hexatic B liquid crystalline phase to form [52]. Thus, between 10 and 75 wt% of methyl stearate (H(CH2)i7C02CH3) in methyl palmitate (H(CH2)i5C02CH3), an phase whose birefringent pattern is indistinguishable from that of BS can be detected. From X-ray diffraction measurements, the layer spacing of a 1 1 mixture in its phase, 25.7 A, is 2.5 A longer than that found in the lower temperature (and more densely packed) solid phase. 

There are many other examples of the dramatic effects that small groups and their positions along the main chain of an MLC can have on phase behavior. Demonstrations of both induction and destruction of liquid crystallinity have been documented when even small groups like methyl are added [148-150] they can affect packing arrangements by influencing conformations of single molecules and electrostatic interactions between molecules. Unfortunately, the manifestations of these perturbations on MLCs and PLCs are not easily related in many cases. 

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Logarithms of relative rate constants for the hydrogenolysis of alkyl alkanoates were successfully correlated with a relationship derived from Equation 13 (lA) The results suggested a dependence on branching but due to collinearity were not conclusive. 

Alkyl alkanoates are reduced only at very negative potentials so that preparative scale experiments at mercury or lead cathodes are not successful. Phenyl alkanoates afford 30-36% yields of the alkan-l-ol under acid conditions [148]. Preparative scale reduction of methyl alkanoates is best achieved at a magnesium cathode in tetrahydrofuran containing tm-butanol as proton donor. The reaction is carried out in an undivided cell with a sacrificial magnesium anode and affords the alkan-l-ol in good yields [151]. In the absence of a proton donor and in the presence of chlorotrimethylsilane, acyloin derivatives 30 arc formed in a process related to the acyloin condensation of esters using sodium in xylene [152], Radical-anions formed initially can be trapped by intramolecular addition to an alkene function in substrates such as 31 to give aiicyclic products [151]. 

Acid hydrolysis of l-(2-alkyl-l-oxoalkyl)-a,a-dimethyl-2-pyrrolidinemethanols 2 furnishes 2-alkyl-alkanoic acids 4 in 76-99 % ee, along with the protonated chiral auxiliary 9. The latter can be recycled by acylation to yield l-acyl-a,a-dimethyl-2-pyrrolidinemethanols19-22. Although slightly more drastic conditions are required for hydrolysis of these derivatives compared with the conditions used for l-acyl-2-pyrrolidinemethanols (see Section 1.1.1.3.3.4.1.2.1.), racemiza-tion of the resulting acids does not seem to be a problem. 

Either enantiomer of a-alkylated alkanoic acids, 3-substituted dihydro-2(3//)-furanones and 3-substituted tetrahydro-2//-pyran-2-ones with known absolute configuration and high optical purities can be obtained from metalation and alkylation of chiral 4,5-dihydrooxazoles (see Section 1.1.1.4.3.). 

A simplified, one-pot, sequential alkylation furnishes both enantiomers of a-alkylated alkanoic acids starting from the same chiral 2-methyl-4,5-dihydrooxazole, however, chemical yields and enantiomeric excesses are generally lower than in the stepwise approach2. 

This model is based on Sw data spanning 5 log units. Nirmalakhandan and Speece [36,37] discuss the model s validity and robustness in detail. They performed a test using experimental Sw data for esters, ethers, and aldehydes that were not included in the training set. They noted reasonably good agreement between experimental and estimated data for the test set and indicated that eq. 11.5.4 is applicable to dialkyl ethers, alkanals, and alkyl alkanoates, but not for ketones, amines, PAHs, and PCBs. Nirmalakhandan and Speece [37] expanded the model above for the PAHs, PCBs, and PCDDs. However, their model has been criticized by Yalkowsky and Mishra for incorrect and omitted data [38]. The revised model is [38]... 

Method of Wakita, Yoshlmoto, Miyamoto, and Watanabe The Wakita et al. method [46] has been derived with a set of 307 liquid compounds, including alkanes, alkenes, alkynes, halogenated alkanes, alkanols, oxoalkanes, alkanones, alkyl alkanoates, alkanethiols, alkanenitriles, nitroalkanes, and substituted benzenes, naphthalenes, and biphenyles. The model equation is... 

The IUPAC rules name esters as alkyl alkanoates. That is, the portion of the ester derived from the alcohol is named as an alkyl group. The portion of the ester that is derived from the carboxylic acid is named as the conjugate base of that acid. It is easy to distinguish these parts. The half derived from the carboxylic acid has the carbonyl group. Pentyl ethanoate, or pentyl acetate, is one ester used as artificial banana flavoring. Figure 11.51 shows three ester nomenclature examples. 

Alkylation of the 2-methyl-2-oxazoline (base/electrophile) results in homologated 2-oxazolines. A second alkylation sequence proceeds with asymmetric induction and results in the formation of highly substituted chiral 2-alkyl alkanoic acids. Use of ethylene oxide as the electrophile in this process allows for the formation of chiral a-substituted y-butyrolactones and a-substituted 7-valerolactones with good stereoselectivity (60-80% ee eq 3). ... 

Esters (RCOOR ) are named as alkyl alkanoates. The alkyl group is named first, followed by the acyl group, with -ate replacing -yl of the acyl group. 

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