Methylene unit values

Methylene unit values from the single or multiple peaks that result from the GC separation on 180 cm X 6.3 mm OD glass column packed with 5% SE-30 on 100/200 mesh Chromosorb W(HP) programmed from 100° to 325°C at 10°C/min. 

Horii et al, (1965a) and Blakley (1966) introduced, at about the same time, trimethylsilylation of both carboxyl and hydroxyl groups to provide suitable volatile derivatives of aromatic acids. As polyester phases are not suitable for TMS derivatives, silicone columns (SE-52 and SE-60) were used, these workers (Horii et al., 1965a) claiming to obtain single symmetrical peaks for most of 40 aromatic acids tested. 2,3-Dihydroxybenzoic acid yields two peaks (Blakley, 1966), which result presumably from partial steric interference in the trimethylsilylation reaction (HMDS/TMCS). The methylene unit values of TMS derivatives of aromatic acids and an evaluation of their elution order on both OV-1 and OV-17 phases have also been reported (Butts, 1972). 

Ramsdell and Tanaka (1977) studied the GC properties of 21 acylglycines as their methyl esters, on three different column phases, 5 per cent OV-1,10 per cent OV-17 and 5 per cent neopentylglycol adipate (NPGA) all on Anachrom (80-90 mesh) support. The methylene unit values for this study are reproduced in Table 4.1. The aliphatic acylglycines run well as single peaks on each column and, with the exception of acrylylglycine and propionylglycine on OV-1, are all resolved. 

Table 4.1 Methylene unit values for methyl esters of acylglycines (Data taken from Ramsdell and Tanaka, 1977)...

Table 4.2 Methylene unit values of the mono-TMS derivatives of V-acylglycines on 5 per cent OV-1 column (Data taken from Rowley and Gerritsen, 1975)...

A. An alphabetical order of compounds with each mass spectrum listed as its thirteen most abundant ions with their individual relative intensity values recorded below the mass number. The molecular weight, relative retention time (n-tetracosane as internal standard) and methylene unit value are listed under the headings MW, RRT and MU respectively. 

Gas-chromatographic retention times were determined from compounds run on a 1.83 m x 0.004 m glass column packed with 10% OVIOI on HP Chromsorb W (80-100 mesh) using a temperature programme of 110-285°C at 4° min with a 5 min isothermal delay. Retention times are quoted relative to n-tetracosane as internal standard and methylene unit values were determined from the retention times of normal hydrocarbons (C-10,11,12,14,16,18,20, 22, 24, 26) recorded under the same GC conditions as the samples. Retention times which were not recorded are denoted by an asterisk ( ). 

The y relaxation takes place at the lowest temperature, overlaps with the )3 relaxation (Fig. 15), and coincides in location and activation energy with the typical y relaxation of polyethylene [35,36], and also of polyethers [37], and polyesters [38] with three or more consecutive methylene units. It appears, for 3 Hz and tan6 basis, at - 120°C (P7MB) and - 126°C (P8MB), and its location and activation energy (35-45 kJ mol ) agree with the values of a similar relaxation associated with kink motions of polymethylenic sequences. 

Fig. 14 Experimental (a) and calculated (b) conductance values of Au-n-alkanedithiol-Au junctions vs number n of methylene units in a semilogarithmic representation. The three sets of conductance values - high (H), medium (M), and low (L) - are shown as squares, circles, and triangles. The straight lines were obtained from a linear regression analysis with decay constants (3n defined per methylene (CH2) unit. The conductances of many different, nonequivalent gauche isomers cover the window below the medium values in (b) [64]...

An increase in the number of methylene units in alkyl benzene did not significantly affect the 7t-energy effect on their retention, but the enthalpy effect increased dramatically [80]. This means that a hydro-phobic compound can be adsorbed directly onto an octadecyl-bonded silica gel. The value of enthalpy effect of a methylene unit in alkyl benzene was calculated to be 500 cal/mol. 

PTT, with three methylene units in its glycol moiety, is called an odd-numbered polyester. It is often compared to the even-numbered polyesters such as PET and PBT for the odd-even effect on their properties. Although this effect is well established for many polycondensation polymers such as polyamides, where the number of methylene units in the chemical structures determines the extent of hydrogen bonding between neighboring chains and thus their polymer properties, neighboring chain interactions in polyesters are weak dispersive, dipole interactions. We have found that many PET, PTT and PBT properties do not follow the odd-even effect. While the PTT heat of fusion and glass transition temperature have values between those of PET and PBT, properties such as modulus... 

METHYLENE UNIT (MU) VALUES OF MENTHOL STEREOISOMERS MENTHOGLYCOL AND NEOMENTHOGLYCOL [35]... 

Alkanethiol-based or alkylsiloxane-based SAMs have been profitably employed in all these instances to probe the distance effect in electron-transfer dynamics. The thiol-based SAMs have the virtue that the spacer length can be predictably altered simply by varying the number of methylene units in the chain. The distance dependence of is embodied in the parameter f, the decay coefficient (for a critical discussion of the subtleties involved in the extraction and interpretation of this parameter, see Ref. [399]). A value of 0.49 0.07 has been reported for f for n-InP-alkanethiol-ferrocyanide interfaces [403]. This value is smaller than its counterpart for corresponding films on gold surfaces which range from 0.6 to 1.1 per methylene unit. The reason for this difference is not entirely clear, although several hypotheses were advanced by the authors [403]. 

The thermodynamic properties of the phase transitions of LC copolymers are not yet well documented, even though odd-odd combinations in the number of methylene units of the spacers seem to have lower AS values, indicating a less ordered structure. Copolymers of mixed mesogenic units also have not been sufTiciently studied to make an attempt to analyze the data... 

---