Intramolecular forces, comparison

In molecular covalent compounds, intermolecular forces are very weak in comparison with intramolecular forces. For this reason, most covalent substances with a low molecular mass are gaseous at room temperature. Others, with higher molecular masses may be liquids or solids, though with relatively low melting and boiling points. 

You have learned that pure covalent compounds are not held together by ionic bonds in lattice structures. They do form liquids and solids at low temperatures, however. Something must hold the molecules together when a covalent compound is in its liquid or solid state. The forces that bond the atoms to each other within a molecule are called intramolecular forces. Covalent bonds are intramolecular forces. In comparison, the forces that bond molecules to each other are called intermolecular forces. 

Neutron time-of-flight spectra (2<5) for Nylon-6 are given in Fig. 10. A comparison of NIS and infrared data for Nylon-6 (5, 16, 18, 37), and NIS and infrared spectra 30) for n-heptane is given in Table 3. The vibrations of the -( 112)5- segments in Nylon-6 are expected to occur below 600 cm-, where the intramolecular C-C-C deformation and C-C torsional modes in n-paraffins have been shown to occur (7). In view of the transferability established for the intramolecular force constants among the n-paraffins 33), it was of interest to test the degree to which they could be transferred to the —( 112)5 groups of Nylon-6. 

These intermolecular forces which hold the molecules together in the solid state are in general weak in molecular crystals in comparison to the intramolecular forces. Molecular crystals derive their name from the fact that the molecules as such remain intact within the crystals and thus directly determine the physical... 

The physicochemical properties of the ILs, like all other materials, depend upon the intermolecular and intramolecular forces and, hence, upon the stmcture of the cation and the anioa A significant number of investigations have been conducted for AILs on the relationship between their pltysicochemical properties and the stmcture of their cation and anioa In comparison, we believe there are few investigations that similarly observe trends for series of... 

Figure 11.2 Comparison of a covalent bond (an intramolecular force) and an intermolecular attraction. 

A somewhat different opinion on the reason for the the above-discussed disparity between activation barriers was expressed in Ref. [91] to the effect that a dimer may be compressed in crystal packing in order to maintain its structure on balance of inter- and intramolecular forces. Thus, the equilibrium structure of the dimer in the crystal may differ from that in the isolated state . Calculations by a molecular mechanics method gave some substance to this assumption the O O distance in a dimer was shown to be compressed approximately 0.03-0.04 A in the crystal in comparison with an isolated dimer. As a result, the calculated activation barrier is reduced though not so drastically. 

Intramolecular charge transfer in 4-nitropyridine N-oxide has been investigated by spectroscopic methods and by comparison with AMI and MNDO semi-empirical methods to obtain the vibrational force field225. The results obtained indicate that protic solvents (water, methanol) favour the mesomeric form 97 which is also favoured in the crystal, by an internal interaction between the nitro and TV-oxide groups226. 

Intramolecular Ru(II) to Cu(II) ET rates have been measured in two other blue copper proteins, stellacyanin [42, 43] and azurin [9, 13, 28]. Pseudomonas aeruginosa azurin has been ruthenated at His83 [13] (Fig. 5). The intramolecular Ru(II) to Cu(II) ET rate of 1.9 s was found to be independent of temperature [28]. The Cu reorganization enthalpy was estimated to be < 7 kcal/mol [13, 28], a value confirming that blue copper is structured for efficient ET. Again, a blue copper ET rate is low in comparison with heme protein rates over similar distances (at similar driving forces) (Table 1). 

The intramolecular 4 + 3-, 3 + 3-, 4 + 2-, and 3 + 2-cycloaddition reactions of cyclic and acyclic allylic cations have been reviewed, together with methods for their generation by thermal and photochemical routes.109 The synthetic uses of cycloaddition reactions of oxyallyl cations, generated from polybromo and some other substrates, have also been summarized seven-membered rings result from 4 + 3-cycloadditions of these with dienes.110 The use of heteroatom-stabilized allylic cations in 4 + 3-cycloaddition reactions is also the subject of a new experimental study.111 The one-bond nucleophilicities (N values) of some monomethyl- and dimethyl-substituted buta-1,3-dienes have been estimated from the kinetics of their reactions with benzhydryl cations to form allylic species.112 Calculations on allyl cations have been used in a comparison of empirical force field and ab initio calculational methods.113... 

By comparison of the dynamic viscosity expressions without and with internal viscosity [see Eqs. (3.1.15) and (3.3.16), respectively], we see that in the former case the sum tends to zero for large co, unlike in the latter we conclude that in the presence of internal viscosity the dynamic viscosity deviates from what is commonly regarded as a general law. The reason lies in the fact that with internal viscosity the intramolecular tension contains a contribution depending on x h,t), unlike the other models where it depends on the elastic force only, that is, on x h,t). 

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