phenol + h2o

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    3986
  • This page looks at the structure and physical properties of phenol (very old name: carbolic acid). Phenol is the simplest thành viên of a family of compounds in which an -OH group is attached directly to tướng a benzene ring.

    The structure of phenol

    The simplest way to tướng draw the structure of phenol is:

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    phenol.gif

    . . . but to tướng understand phenol properly, you need to tướng dig a bit deeper phàn nàn this.

    There is an interaction between the delocalized electrons in the benzene ring and one of the lone pairs on the oxygen atom. This has an important effect on both the properties of the ring and of the -OH group. One of the lone pairs on the oxygen overlaps with the delocalized ring electron system . . .

    phenoldeloc1.gif

    . . . giving a structure rather lượt thích this:

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    phenoldeloc2.gif

    The donation of the oxygen's lone pair into the ring system increases the electron mật độ trùng lặp từ khóa around the ring. That makes the ring much more reactive phàn nàn it is in benzene itself. That is explored in another page in this phenol section. It also helps to tướng make the -OH group's hydrogen a lot more acidic phàn nàn it is in alcohols. That will also be explored elsewhere in this section.

    Physical properties

    Pure phenol is a white crystalline solid, smelling of disinfectant. It has to tướng be handled with great care because it causes immediate white blistering to tướng the skin. The crystals are often rather wet and discolored.

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    Melting and boiling points

    It is useful to tướng compare phenol's melting and boiling points with those of methylbenzene (toluene). Both molecules contain the same number of electrons and are a very similar shape. That means that the intermolecular attractions due to tướng khẩn khoản der Waals dispersion forces are going to tướng be very similar.

    melting point (°C) boiling point (°C)
    C6H5OH 40 - 43 182
    C6H5CH3 -95.0 111

    The reason for the higher values for phenol is in part due to tướng permanent dipole-dipole attractions due to tướng the electronegativity of the oxygen - but is mainly due to tướng hydrogen bonding. Hydrogen bonds can size between a lone pair on an oxygen on one molecule and the hydrogen on the -OH group of one of its neighbors.

    Solubility in water

    Phenol is moderately soluble in water - about 8 g of phenol will dissolve in 100 g of water. If you try to tướng dissolve more phàn nàn this, you get two layers of liquid. The top layer is a solution of phenol in water, and the bottom one a solution of water in phenol. Phenol is somewhat soluble in water because of its ability to tướng size hydrogen bonds with the water.