The apparent molecular association of some aliphatic acids

Broughton, George

doi:10.1039/tf9343000367

Cited by 14 publications

(4 citation statements)

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“…pentadecanoic, myristic, tridecanoic, lauric, undecanoic and capric acids. Figure 3 shows the phenomenon of dimerization, as pointed out previously [1,7,8]. 2, the experimental points fall into an ideal curve, and this fact 1 At supports our hypothesis.…”

Section: Crvoscopic Measurementssupporting

confidence: 87%

Thermodynamic properties of organic compounds. Note III

Berchiesi

Leonesi

Cingolani

1975

Journal of Thermal Analysis

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Section: Crvoscopic Measurementssupporting

confidence: 87%

Thermodynamic properties of organic compounds. Note III

Berchiesi

Leonesi

Cingolani

1975

Journal of Thermal Analysis

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“…From these latest results it would appear th at the adsorption and migration of molecules on crystal faces is extensive, in support of the theoretical predictions of Burton, Cabrera & Frank (1951). The earlier evidence (Dawson & Vand 1951) in favour of packing of steps in the case of w-hexatriacontane must, in the light of…”

Section: Discussion (< A)supporting

confidence: 74%

“…The first compound chosen for study was stearic acid, C17H9sCOOH (m.p. 69-6° C) both because monocarboxylic acids are known to exist as dimers in solution (the work of Broughton (1934) established the dimeric nature of palmitic acid in cyclohexane), and because stearic acid has a molecular length of approxi mately 25 A and is of a size which makes it possible to distinguish between unimolecular steps, bimolecular steps and multimolecular steps. Stearic acid crystal lizes in at least three polymorphic forms, only two of which are stable at room temperature.…”

Section: Ma T E R Ia L S a N D M E T H O D Smentioning

confidence: 99%

The study of crystal growth with the electron microscope III. Growth-step patterns and the relationship of growth-step height to molecular structure in n -nonatriacontane and in stearic acid

1953

Proc. R. Soc. Lond. A

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The exact relationship between molecular association in solution and growth-step height was obtained from measurements of shadowcast electron micrographs. Crystals of the paraffin n -nonatriacontane, C 39 H 80 , give a value of growth-step height of 45 ± 10 Ȧ, the unimolecular value. Similarly, crystals of stearic acid, C 17 H 35 COOH, give a value of 47 ± 10 Ȧ, the bimolecular value. There is thus strict correspondence between the unimolecular nature of n -nonatriacontane molecules in solution and unimolecular n -nonatriacontane growth-steps and between the bimolecular nature of stearic acid molecules in solution and bimolecular stearic acid growth-steps. In crystals of both compounds, grown from a dislocation of length any multiple of the length of the units in solution, multimolecular growth-steps were not encountered. Instead the growth pattern dissociated into a succession of unimolecular steps in n -nonatriacontane crystals and bimolecular steps in stearic acid crystals. There is thus strong evidence that the size of the unit in solution and not the length of the parent dislocation is the responsible factor in deciding the height of growth-steps. The crystals examined show a variety of growth-step patterns—spirals, layers, halfsteps and flat-tops. In layered crystals which show no sign of spiral growth there is strong internal evidence that the crystals have in fact grown by a spiral mechanism. A series of micrographs showing crystals in a state of transition makes it clear that the screw dislocation responsible for growth has been cancelled out by the formation of an equal and opposite dislocation. Numerous examples of this cancellation process have been encountered either at the end of all growth or as a relapse when one of the dislocations in a pair of the same sense has been cancelled during growth. This evidence for the growth and movement of dislocations in real crystals shows that crystals with molecularly flat surfaces may well be produced by a mechanism based on screw dislocations. The fact that no spiral growth-steps can be observed is no longer adequate proof that a spiral growth mechanism did not produce the crystal in question.

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“…Association tends to increase the solubility of the more insoluble constituent, and would be likely to increase the tendency to mixed-crystal formation. Other studies in this field have been made by Francois (50), Boutaric and Roy (26), and Broughton (29).…”

Section: H Discussionmentioning

confidence: 99%

Low-temperature Crystallization of the Fatty Acids and Glycerides.

Brown¹

1941

Chem. Rev.

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The apparent molecular association of some aliphatic acids

Cited by 14 publications

References 0 publications

Thermodynamic properties of organic compounds. Note III

Thermodynamic properties of organic compounds. Note III

The study of crystal growth with the electron microscope III. Growth-step patterns and the relationship of growth-step height to molecular structure in n -nonatriacontane and in stearic acid

Low-temperature Crystallization of the Fatty Acids and Glycerides.

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