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The two crystal forms for racemic menthol have melting points of 28 °C and 38 °C. Pure (−)-menthol has four crystal forms, of which the most stable is the α form, the familiar broad needles. Pure (−)-menthol has four crystal forms, of which the most stable is the α form, the familiar broad needles.
Menthone is a constituent of the essential oils of pennyroyal, peppermint, corn mint, pelargonium geraniums, and other plant species. [1] In most essential oils, it is a minor component. [5] Menthone was first synthesized by oxidation of menthol in 1881, [6] [needs update] [7] before being found as a component in essential oils in 1891.
The melting point (or, rarely, liquefaction point) of a substance is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depends on pressure and is usually specified at a standard pressure such as 1 atmosphere or 100 kPa.
{{Periodic table (melting point)|state=expanded}} or {{Periodic table (melting point)|state=collapsed}}This template's initial visibility currently defaults to autocollapse, meaning that if there is another collapsible item on the page (a navbox, sidebar, or table with the collapsible attribute), it is hidden apart from its title bar; if not, it is fully visible.
For example, IUPAC has, since 1982, defined standard reference conditions as being 0 °C and 100 kPa (1 bar), in contrast to its old standard of 0 °C and 101.325 kPa (1 atm). [2] The new value is the mean atmospheric pressure at an altitude of about 112 metres, which is closer to the worldwide median altitude of human habitation (194 m).
The Gmelin rare earths handbook lists 1522 °C and 1550 °C as two melting points given in the literature, the most recent reference [Handbook on the chemistry and physics of rare earths, vol.12 (1989)] is given with 1529 °C.
Up to 99.63 °C (the boiling point of water at 0.1 MPa), at this pressure water exists as a liquid. Above that, it exists as water vapor. Note that the boiling point of 100.0 °C is at a pressure of 0.101325 MPa (1 atm), which is the average atmospheric pressure.