Constitution, molecular

The common elements in the cited examples are the mechanical characteristics and the insulation properties. These advantages come, not only from macroscopic configuration of these materials (the hollow cylindrical structure of stubble for instance), but, mainly, from their microscopic structure. Most the vegetal fibres can be described by two models wood fibres and cotton fibres, which will be presented later. In order to better understand the mechanical properties of these fibres, let us first consider their molecular constitution, then their hierarchical structure. 

All natural fibres are constituted essentially of four kinds of components  

Cellulose is by far the most abundant component, especially in cotton fibres. This biopolymer is constituted of cellobiose (repetitive unit), which is composed 

Hemicelluloses are constituted of different hexoses and pentoses glucose, mannose, xylose, etc. Since these heteropolysaccharides are often branched polymers, they cannot constitute crystalline structures. However, their function in the constitution of natural fibres is crucial. Together with lignin, they constitute the bonding matrix of the cellulose microfibres. 

Lignin is an amorphous non-polar macromolecule, constituted of phenylpropane units. The structure of lignin depends on the source. Moreover, the extraction method modifies the structure of the lignin prior to analysis. Recent studies (Banoub et al., 2007 Forss and Fremer, 2000) have shown fundamental differences with the known structures of lignin. 

---

Maxwell J C 1874 Van der Waals on the continuity of the gaseous and liquid states Nature 10 477 Maxwell J C 1875 On the dynamical evidence of the molecular constitution of bodies Nature 11 357... 

It is convenient to have some uniform method of representing the composition of a solution, and for this purpose use is made of the so-called concentration of a component, which may be referred to the total mass, or to the total volume, or to the molecular constitution. 

The state of the surface of a brittle solid has been found to exert a considerable influence on the mechanical behaviour observed it is at least as important as the underlying molecular constitution in this regard. The presence of microscopic scratches, voids, or other imperfections will seriously weaken the tensile strength of specimens of glassy polymer, such as poly(methyl methacrylate) at ambient temperatures. 

Errera, J., Sherrill, M. L. (1929). Dipole moment and molecular constitution. In P. Debye (Ed.), Dipolmoment und Chemische Struktur [Dipole Moment and Chemical Structure], Leipzig Hirzel. 

Molecules aim at being packed as closely as possible in the crystal 26 28). Bulkiness of a molecule, however, is an impediment. It presupposes a molecular constitution rather unbalanced in its spatial dimensions and a certain extent of conformational rigidity. Here we encounter a parallel to an everyday occurrence trunks can easily be arranged to a compact ordered stack, unlike bulky root stocks which cannot. The... 

Fig. 11. Graphic development (a)-(c) of a molecular constitution (coordinatoclathrate host 1) compared to a pair of scissors...

A single crystal X-ray structure analysis of 8 (Fig. 4) confirms the molecular constitution of the compound deduced by spectroscopic methods and shows further structural details. The molecule is dimeric with a Mn-C15 ( -carbyne) bond length of 1.857(2) A and a Mn-Mn bond distance of 2.565(1) A the latter one is typical for a Mn-Mn single bond [13]. The Mn-C15 (carbyne) bond is short compared to known Mn-C single bonds, for example that in (OC)4Mn-C(C00Et)C(HgBr)C(0Et)0 is found to be 2.051(26) A [13b], For the acyclic carbyne complex [Cp(CO)2Mn = C-CH=CPh2]+ BF4 the MnC distance is 1.665(5) A [14] comparable values for... 

Ultraviolet spectroscopic studies on bagasse native lignin demonstrated that (a) the native and enzymatically liberated lignins are identical, and (b) that it has a molecular constitution somewhat different from other lignins (54), (107), (111). (See Fig. 2.)... 

Second, considerable effort has been expended to create 13C NMR reference data systems that will enable spectroscopists to extract structural information from their experimental results by comparing them with documented spectra of related compounds data banks stored in computers have been compiled and are accessible for substructure searches (510-519). The advent of these facilities means that SCS evaluations have been-at least in principle-outstripped in an important field of their application, namely in their use for establishing molecular constitution and assigning signals. In cases of doubt one should rely... 

The Simultaneous Representation of Molecular Constitution and Stereochemical Features and their Interconversions... 

Molecular Constitutive Equations for Polymer Melts in Viscoelastic Flow Solvers... 

Note It is important to assign the correct charge and radical state to all species encountered and to carefully track them through a fragmentation scheme. Otherwise, impossible fragmentation pathways may be formulated, thereby misleading the assignment of elemental composition and molecular constitution. 

Sugden J.G.S. cxxv. 1177, 1924 cxxvii. 1525, 1868, 1925) has compared the molecular volumes of substances under conditions such that they possess identical surface tensions and has shown that they are determined by the molecular constitutions of the substances. In obtaining the parachor P Sugden makes use of the approximate relationship between free surface energy and density noted by Macleod Trans. Farad. Soc. xix. 38, 1923) a = c(pi- p y... 

Thiophene is present in the benzene fraction from the distillation of coal tar. As with pyrrole and furan, the same type of resonance forms contribute to its overall molecular constitution, and the compound is aromatic in character. There is a difference between thiophene and furan, however, because sulfur is less electronegative than oxygen. Thus, the chemistry of thiophene tends to be closer to that of pyrrole than to that of furan. For example, thiophene does not enter easily into [4 + 2] cycloaddition reactions and quite severe conditions, high pressure (15 bar) and a temperature of 100 C, are necessary in order to force a cycloaddition between it and maleic anhydride. 

---