Molecular and structural formula of phenol

Phenols are the common name for aromatic alcohols. By their properties, substances are weak acids. Of great practical importance are many homologues of hydroxybenzene C ₆ H ₅ 0H (phenol formula) - the simplest representative of the class. Let us dwell on this in more detail.

Phenols. General formula and classification

The general formula of organic substances related to aromatic alcohols is R-OH. The molecules of phenols and cresols proper are formed by the radical - phenyl C6H5, with which one or several hydroxyl groups OH (hydroxy groups) are directly connected. By their number in a molecule, phenols are classified into single, double and polyatomic. Monatomic compounds of this type are phenol and cresol. The most common among polyhydric hydroxybenzenes are naphthols, which contain 2 fused nuclei.

Phenol is a representative of aromatic alcohols

Phenol was known to textile workers already in the XVIII century: weavers used it as a dye. In the distillation of coal tar in 1834, German chemist F. Runge selected crystals of this substance with a characteristic sweetish smell. The Latin name of coal is carbo, so the compound was called carbolic acid ( carbolic acid ). The German researcher failed to determine the composition of the substance. The molecular formula of phenol was established in 1842 by O. Laurent, who considered the carbolic derivative of benzene. For the new acid used the name "phenyl". Charles Gerard determined that the substance is an alcohol, and called it phenol. The initial application areas of the compound are medicine, tanning of leather, production of synthetic dyes. Characteristics of the substance:

• The rational chemical formula is C ₆ H ₅ OH.
• The molecular weight of the compound is 94.11 a. eat.
• The gross formula, reflecting the composition, is C ₆ H ₆ O.

The electronic and spatial structure of the phenol molecule

The cyclic structural formula of benzene was proposed by the German organic chemist F. Kekule in 1865, and shortly before it - I. Loschmidt. Scientists represented a molecule of organic matter in the form of a regular hexagon with alternating simple and double bonds. According to modern ideas, the aromatic nucleus is a special kind of ring structure, called "conjugated connection".

Six carbon atoms C experience the process of sp ² -hybridization of electronic orbitals. The p-electron clouds, which do not participate in the formation of C-C bonds, overlap over and under the plane of the nucleus of the molecule. There are two parts of a common electronic cloud, which covers the entire ring. The structural formula of phenol can look different, given the historical approach to the description of the structure of benzene. To emphasize the unsaturated nature of aromatic hydrocarbons, three of the six bonds are conventionally considered to be double, which are interspersed with three simple ones.

Polarization of the bond in the hydroxy group

In the simplest aromatic hydrocarbon - benzene C ₆ H ₆ - the electron cloud is symmetrical. The phenol formula differs by one hydroxy group. The presence of hydroxyl disrupts symmetry, which is reflected in the properties of the substance. The bond between oxygen and hydrogen in the hydroxy group is polar covalent. The displacement of the general pair of electrons to the oxygen atom leads to the appearance of a negative charge (partial charge) on it. Hydrogen is deprived of an electron and acquires a partial charge of "+". In addition, oxygen in the O-H group is the owner of two unshared electron pairs. One of them is attracted by an electronic cloud of the aromatic nucleus. For this reason, the bond becomes more polarized, the hydrogen atom is more readily replaced by metals. The models give an idea of the asymmetric nature of the phenol molecule.

Peculiarities of the interaction of atoms in phenol

A single electron cloud of the aromatic nucleus in the phenol molecule interacts with the hydroxyl group. There is a phenomenon called conjugation, as a result of which the natural pair of electrons of the oxygen atom of the hydroxy group is attracted to the benzene cycle system. The decrease in the negative charge is compensated for by an even greater polarization of the bond in the O-H group.

The electronic distribution system also changes in the aromatic nucleus. It decreases on carbon, which is associated with oxygen, and rises near the nearest atoms in ortho-positions (2 and 6). The conjugation causes the accumulation of the charge "-" on them. Further displacement of density is its motion from atoms in meta-positions (3 and 5) to carbon in the para-position (4). The phenol formula for the convenience of studying conjugation and mutual influence usually contains the numbering of the atoms of the benzene ring.

Explanation of the chemical properties of phenol on the basis of its electronic structure

The processes of conjugation of the aromatic nucleus and hydroxyl affect the properties of both particles and the entire substance. For example, the high electron density of atoms in the ortho- and para positions (2, 4, 6) makes the C-H bonds of the aromatic ring of phenol more reactive. The negative charge of carbon atoms in meta-positions decreases (3 and 5). Attack of electrophilic particles in chemical reactions subjected to carbon, located in the ortho- and para-positions. In the bromination reaction of benzene, the changes occur with strong heating and the presence of a catalyst. A monohalogeno derivative, bromobenzene, is formed. The phenol formula allows the substance to react with bromine almost instantaneously without heating the mixture.

The aromatic nucleus affects the polarity of the bond in the hydroxy group, increasing it. The hydrogen atom becomes more mobile, in comparison with the limiting alcohols. Phenol reacts with alkalis, forming salts - phenolates. Ethanol does not react with alkalis, or rather, reaction products - ethanolates - decompose. Chemically, phenols are stronger acids than alcohols.

Representatives of the class of aromatic alcohols

The gross formula for the homologue of phenol-cresol (methylphenol, hydroxytoluene) is C ₇ H ₈ O. The substance in natural raw materials often accompanies phenol, also has antiseptic properties. Other phenol homologues:

• Pyrocatechin (1,2-hydroxybenzene). The chemical formula is C ₆ H ₄ (OH) ₂ .
• Resorcinol (1,3-hydroxybenzene) -C6H4 (OH) ₂ .
• Pyrogallol (1,2,3-trihydroxybenzene) -C6H3 (OH) ₃ .
• Naphthol. The gross formula of the substance is C ₁₀ H ₇ OH. It is used in the manufacture of dyes, medicines, fragrant compounds.
• Timol (2-isopropyl-5-methylphenol). The chemical formula is C ₆ H ₃ CH ₃ (OH) (C ₃ H ₇ ). It is used in the chemistry of organic synthesis, medicine.
• Vanillin, in addition to the phenolic radical, contains an ether group and an aldehyde residue. The gross formula for the compound is C ₈ H ₈ O ₃ . Vanillin is widely used as an artificial fragrance.

The formula for the reagent for the recognition of phenols

The qualitative determination of phenol can be carried out with the help of bromine. As a result of the substitution reaction, a white precipitate of tribromophenol precipitates. Pyrocatechin (1,2-hydroxybenzene) is colored green in the presence of dissolved ferric chloride. With the same reagent, phenol reacts chemically, and triphenolate, having a purple color, is formed. A qualitative reaction to resorcinol is the appearance of a dark violet staining in the presence of ferric chloride. Gradually, the color of the solution becomes black. The reagent formula, which serves to recognize phenol and some of its homologues, is FeCl ₃ (iron (III) chloride).

Hydroxybenzene, naphthol, thymol are all phenols. The general formula and composition of the substances makes it possible to determine whether these compounds belong to the aromatic series. All organic substances containing in their formula the phenyl radical C ₆ H ₅ , to which the hydroxy groups are directly attached, exhibit special properties. They differ from alcohols by a better expressed acidity. Compared with the substances of the homologous benzene series , phenols are more active chemical compounds.