Dimerization alcohols

Typical specifications for commercially available amyl alcohols (104) are given in Table 4. The impurities typically present are other monomeric alcohols, dimeric alcohols, acetals, and several miscellaneous substances. The alcohols are substantially free of suspended matter. 

Tyn-Calus This correlation requires data in the form of molar volumes and parachors = ViCp (a property which, over moderate temperature ranges, is nearly constant), measured at the same temperature (not necessarily the temperature of interest). The parachors for the components may also be evaluated at different temperatures from each other. Quale has compiled values of fj for many chemicals. Group contribution methods are available for estimation purposes (Reid et al.). The following suggestions were made by Reid et al. The correlation is constrained to cases in which fig < 30 cP. If the solute is water or if the solute is an organic acid and the solvent is not water or a short-chain alcohol, dimerization of the solute A should be assumed for purposes of estimating its volume and parachor. For example, the appropriate values for water as solute at 25°C are = 37.4 cmVmol and yn = 105.2 cm g Vs mol. Finally, if the solute is nonpolar, the solvent volume and parachor should be multiplied by 8 Ig. 

Would you expect the OH stretching frequencies in 2,3-dimethyl-2,3-butanediol to be shifted from the value in tert-butyl alcohol, even in dilute solution. Identify the OH stretching frequencies in the diol and compare them to tert-butyl alcohol. Rationalize your observations by comparing the geometry of the diol with those of tert-butyl alcohol and tert-butyl alcohol dimer. 

Figure 1. Illustration of lone electron pair preferences in alcohol dimers, cooperative and anticooperative binding sites for a third monomer, ring strain and steric repulsion in alcohol trimers, alternation of residues in alcohol tetramers, and chain, branch, and cyclic hydrogen bond topologies in larger clusters.

T. Scharge, D. Luckhaus, and M. A. Suhm, Observation and quantification of the hydrogen bond effect on O H overtone intensities in an alcohol dimer. Chem. Phys. 346,167 175(2008). 

A. Aspiala, T. Lotta, J. Murto, and M. Rasanen, IR induced processes for allyl alcohol dimers involving an intermolecular OH. .. it bond in low temperature matrices. Chem. Phys. Lett. 112, 469 472 (1984). 

Class (3) reactions include proton-transfer reactions of solvent holes in cyclohexane and methylcyclohexane [71,74,75]. The corresponding rate constants are 10-30% of the fastest class (1) reactions. Class (4) reactions include proton-transfer reactions in trans-decalin and cis-trans decalin mixtures [77]. Proton transfer from the decalin hole to aliphatic alcohol results in the formation of a C-centered decalyl radical. The proton affinity of this radical is comparable to that of a single alcohol molecule. However, it is less than the proton affinity of an alcohol dimer. Consequently, a complex of the radical cation and alcohol monomer is relatively stable toward proton transfer when such a complex encounters a second alcohol molecule, the radical cation rapidly deprotonates. Metastable complexes with natural lifetimes between 24 nsec (2-propanol) and 90 nsec (tert-butanol) were observed in liquid cis- and tra 5-decalins at 25°C [77]. The rate of the complexation is one-half of that for class (1) reactions the overall decay rate is limited by slow proton transfer in the 1 1 complex. The rate constant of unimolecular decay is (5-10) x 10 sec for primary alcohols, bimolecular decay via proton transfer to the alcohol dimer prevails. Only for secondary and ternary alcohols is the equilibrium reached sufficiently slowly that it can be observed at 25 °C on a time scale of > 10 nsec. There is a striking similarity between the formation of alcohol complexes with the solvent holes (in decalins) and solvent anions (in sc CO2). 

Change-transfer complexes of solute-alcohol stoichiometry 1 2 have been reported by Walker, Bednar, and Lumry3 for indole and certain methyl derivatives (M) in mixtures of associating solvents n-butanol and methanol (Q) with n-pentane these authors introduced the term exciplex to describe the emitter of the red-shifted structureless fluorescence band which increases in intensity with the alcohol content of the mixed solvent. The shift of the exciplex band to longer wavelengths as the solvent polarity is increased, described by Eq. (15), confirms the dipolar nature of the complex that must have the structure M+Q2. No emission corresponding to the 1 1 complex is observed in these systems which indicates (but does not prove) that the photo-association involves the alcohol dimer. The complex stoichiometry M+Q determined from (Eqs. 9, 10, and 12)... 

The lignans are a large group of plant phenolics, biosynthesized from the union of two phenylpropane molecules e.g., both matairesinol (Centaurea species, family Asteraceae) and podophyllotoxin Podophyllum peltatum, family Berberidaceae) are formed from the phenylpropane coniferyl alcohol. Lignans are essentially cinnamoyl alcohol dimers, though further cyclization and other structural modifications result in various structural types, e.g. dibenzylbutyrolactone and epoxy lignan. 

In the case of cycloheptyl nitrite and cyclooctyl nitrite, the 4-nitroso-l-cyclic alcohol dimers expected from the Barton reaction are isolated. 

Fig, 4. Equilibrium constant, Kj, for formation of alcohol dimers as a function of temperature. Kx =... 

Cm, Xd> Xm arc concentrations and mole fractions, respectively, of dimer and monomer em° is the absorption coefficient of the monomer (found by extrapolating em to C=0 and Kx KC for Cd4. We found values of K for each of the alcohols at a series of temperatures from —10° to +45°C. A plot of log10 K vs. IjT is given in Fig. 4. There is considerable scatter, but the trend in each case is roughly linear, within the limits of error. From the slopes of the lines the heats of formation of the alcohol dimers were calculated and are listed in Table 1. 

The major results of this work are (1) the definite establishment of the presence of dimers in the three alcohols (2) the determination of heats of formation of the dimers and (3) the s,-imort for a cyclic structure of the alcohol dimer. 

The main products of coniferyl alcohol dimerization by peroxidase (Scheme XI) are the neolignans, pinoresinol (XXVII), dehydrodiconiferyl alcohol (XXVni) and guaiacylglycerol-P-O-coniferyl alcohol ether... 

Cinnamyl alcohol dimers are not the end products of the pathway, and so they may be oxidized by peroxidases to yield a growing lignin polymer... 

Use SpartanView to measure the 0-H bond distance and identify the 0-H stretching vibration of (ert-hutyl alcohol. Next, measure the O—H bond distances and identify the two stretching vibrations in tert-butyl alcohol dimer. How does dimerization affect the hydrogen-bonded -OH group, and how does it affect the other -OH group ... 

Completion of the monomeric unit was achieved via Swem oxidation and Arbuzov reaction with trimethylphosphite to give the phosphonate 75 in 31% overall yield from the resolved amino alcohol. Dimeric olefination was effected upon deprotonation to yield the macrocycle 76, which could be converted in 81% yield to optically active vermiculine (56) via sequential cleavage of the thioketal and ketal protecting groups. 

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