Boiling point intramolecular

Methyl salicylate is the methyl ester of o hydroxybenzoic acid Intramolecular (rather than mtermolecular) hydrogen bonding is responsible for its relatively low boiling point... 

The location of the hydroxyl and aldehyde groups ortho to one another in saUcylaldehyde permits intramolecular hydrogen bonding, and this results in the lower melting point and boiling point and the higher acid dissociation constant observed relative to -hydroxybenzaldehyde. 

Some ortho-substituted phenols, such as o-nitrophenol, have significantly lower-boiling points than those of the rneta and para isomers. This is because the intramolecular hydrogen bond that forms between the hydroxyl group and the substituent partially compensates for the energy required to go from the liquid state to the vapor. 

The melting and boiling points of carboxylic acids are much higher than would be expeeted on the basis of their molecular weights. The usual explanation is that they form weak intramolecular bonds. 

To avoid problems with the separation of regiomers, dimethyl acetylene dicarboxylate (DMAD) was chosen as a dienophile. The intermolecular Diels-Alder reactions were performed in refluxing dichlorobenzene (bp 132 °C), while the intramolecular reaction of alkyne tethered pyrazinone required a solvent with a higher boiling point (bromobenzene, bp 156 °C). In the case of 3-methoxy or 3-phenyl pyrazinones a mixture of pyridinones and pyridines was obtained, while for the alkyne tethered analogue only the di-hydrofuropyridinone was isolated as the single reaction product. 

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. 

Discuss the intermolecular and intramolecular forces in N2H4 and C2H4. Based upon the bonding between molecules, which of these two compounds would have a lower boiling point ... 

In some ort/io-substituted phenols, intramolecular H-bonding (chelation) forms a six-membered ring. This inhibits H-bonding with water and reduces solubility in HjO. Since chelation diminishes the mtermolecular H-bonding attraction present in the para and meta isomers, the boiling point is decreased. 

The next main section deals with thermodynamic aspects. It starts by consideration of the intramolecular forces between heterocyclic molecules which influence melting and boiling points, solubility and chromatographic characteristics. This is followed by a section on stability and stabilization, including thermochemistry and conformation of the saturated ring systems, and then a discussion of aromaticity. 

Intramolecular hydrogen bonds form at the expense of intermolecular ones, and intramolecularly hydrogen-bonded phenols have lower boiling points than isomers in which only intermolecular hydrogen-bonding is possible. 

The 1,2,4-triazine core is a synthetically important scaffold because it could be readily transformed into a range of different heterocyclic systems such as pyridines (Sect. 3.1) via intramolecular Diels-Alder reactions with acetylenes. 1,2,4-Triazines have been synthesized by the condensation of 1,2-diketones with acid hydrazides in the presence of NH4OH in acetic acid for up to 24 h at reflux temperature. Microwave dielectric heating in closed vessels allowed the reaction to be performed at 180 °C (60 °C above the boiling point of acetic acid). As a result, the reaction time was reduced to merely 5 minutes. Subsequently, a 48-membered library of 1,2,4-triazines was generated from diverse acyl hydrazides and a-diketones [139]. Two thirds of the desired heterocycles precipitated from the reaction mixture upon cooling with > 75% purity, while the remaining part of the library was purified by preparative LCMS (Scheme 56). 

The product is a mixture of ortho- and para-nitrophenol from which the ortho compound can be separated by steam distillation. A strong intramolecular hydrogen bond reduces the availability of the OH group for intermolecular hydrogen bonds so the ortho compound has a lower boiling point. The remaining pnra-nitrophenol is used in the manufacture of the painkiller paracetamol. 

You can see the difference between intermolecular forces and intramolecular forces in Figure 3.20. Because pure covalent compounds have low melting and boiling points, you know that the intermolecular forces must be very weak compared with the intramolecular forces. It does not take very much energy to break the bonds that hold the molecules to each other. 

Gas-liquid analysis of the product obtained by polycondensation of 1,5-dichlorohexaphenylcyclo-tetrasiloxane with 1,3-dihydroxytetramethyldisiloxane has shown that initial compounds are absent in it and octamethylcyclotetrasiloxane, which would be formed by homocondensation of disiloxane-diol in acidic medium is also absent, but products with higher boiling points, i.e. the products of partial intramolecular condensation are present. In the presence of pyridine, HFC reaction of 1,5-dichlorohexaphenylcyclotetrasiloxane with a,co-dihydroxydimethylsiloxanes proceeds by analogy (at low values of n). 

Macromolecules, submitted). Four isomeric acetonaphthols and 2,4-diaceto-l-naphthol were synthesized by known reactions (27), as simmarized in Scheme I. Purification of these compounds was achieved by a combination of recrystallization, distillation and sublimation, and took advantage of the large differences in boiling point and solubility between intramolecularly H-bonded isomers such as l-aceto-2-naphthol and intermolecul arly H-bonded isomers such as 4-aceto-l-naphthol. The methacrylate esters were synthesized by reaction with methacryloyl chloride in CHgCl y at 0-20°C in the presence of 1 equivalent of pyridine. The monomers are crystalline solids and their structures were verified by IR, NMR and elemental analysis. 

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