What is the chemical formula of butanol

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Alcohols: Physical properties of alcohols

The physical properties of alcohols are largely determined by the OH group. In contrast to the non-polar, organic residue, which is composed of atoms of approximately the same electronegativity (C and H), the high electronegativity of oxygen leads to a polarization of the C-O and the O-H bond and thus to a high dipole moment. This can easily be seen from the electrostatic potential:

Film about the dipole moment of methanol

Tab. 1
Selected physical properties of some alcohols
alcoholMolecular formulaMelting pointboiling pointDipole momentSolubility in water [/ 100]
MethanolCH3OH-97,8 65,0 1.77 D.infinite
EthanolCH3CH2OH-114,7 78,5 1.74 D.infinite
n-PropanolCH3(CH2)2OH-126,5 97,4 1.65 D.infinite
iso-PropanolCH3CH (OH) CH3-89,5 82,4 1.65 D.infinite
n-ButanolCH3(CH2)3OH-89,5 117,3 1.74 D.8,0
tert-Butanol(CH3)3COH25,5 82,2 1.65 D.infinite
n-PentanolCH3(CH2)4OH-79,0 138,0 1.72 D.2,2

Therefore the short-chain alcohols are water-soluble; Methanol, ethanol and propanol can even be mixed with water in any ratio. Straight-chain alcohols with up to ten carbon atoms are liquids and have a typical odor. However, the longer the carbon chain, the more the non-polar carbon chain determines the properties of the alcohol; the properties of the alkane emerge. Long-chain alcohols are no longer soluble in water; they are solid compounds similar to paraffin.

Compared to the corresponding alkanes, the alcohols have very high boiling points. The cause lies in the polarity of the OH group. It enables a special dipole interaction between the individual molecules, which is known as a hydrogen bond. The length of such a bridge is between 169 and 179 and is therefore about twice as long as the O-H bond. It forms between the hydrogen atom of one OH group and the oxygen atom of a second OH group and means that the intermolecular interactions are stronger than with the alkanes. During evaporation, the network-like hydrogen bridges have to be broken. The higher boiling points result from this.

Hydrogen bonds are significantly weaker than covalent bonds. For comparison: the dissociation energy of the O-H bond in methanol is 431. About 20 molecules are needed to split the hydrogen bond between two methanol molecules. The formation of hydrogen bridges can be clearly seen in the following molecular dynamics simulation using the dashed lines:

Molecular dynamics simulation of methanol

Clicking on the preview loads the video of the molecular dynamics simulation: