Physical properties of aldehydes

to aldehydes are organic compounds, which are characterized by a double bond between the carbon and oxygen atoms and two single bonds of the same carbon atom of a hydrocarbon radical represented by the letter R, and a hydrogen atom.Group of atoms & gt; C = O is called the carbonyl group, it is characteristic of all the aldehydes.Many aldehydes have a pleasant smell.They may be prepared from alcohols by dehydrogenation (hydrogen removal), thereby collectively known - aldehydes.Properties are determined by the presence of aldehyde carbonyl group, its location in the molecule, and the length and spatial branched hydrocarbon radical.That is, knowing the name of the substance reflects its structural formula, it is possible to expect certain chemical and physical properties of aldehydes.

There are two main ways of naming aldehydes.The first method is based on the system used by the International Telecommunication Union (IUPAC), it is often called systematic nomenclature.It is based on the fact that the longest chain, which is attached to a carbon atom of the carbonyl group, forms the basis of the aldehyde title, that is, its name comes from the name of the related alkane by replacing the suffix -an suffix -Al (methane - matanal, ethane - ethanalpropane - propanal, butane - butanal and so on).Another method uses the formation of aldehydes title name corresponding carboxylic acid, which as a result of oxidation of the turn (methanal - formic aldehyde, ethanal - acetic aldehyde, propanal - aldehyde is propionaldehyde, butanal - aldehyde oil and so on).

main structural differences between alkanes and aldehydes, the physical properties of aldehydes, is the presence in the past of the carbonyl group (& gt; C = O).This group is responsible for the differences in physical and chemical properties of substances with the same number of carbon atoms or the same molecular weight.These differences are due to the polarization of the carbonyl group & gt; + = Oδ- Sδ.That is, the electron density of carbon atoms is shifted in the direction of an oxygen atom, making the oxygen partial electronegative and electropositive carbon part.To indicate the polarity of the carbonyl group is often used Greek letter delta (δ), this indicates a partial charge.The negative end of a polar molecule is attracted to the positive end of another polar molecule.These can be molecules of the same whether another substance.Aldehydes ketones differs from that in the last carbon of the carbonyl group is connected by single bonds with two hydrocarbon radicals.In this context it is also interesting to compare the physical properties of aldehydes and ketones.It

polar group & gt; C = O affects the physical properties of aldehydes: melting point, boiling point, solubility, dipole moment.Hydrocarbon compounds that contain only hydrogen and carbon atoms, melt and boil at low temperatures.In compounds having a carbonyl group are significantly higher.For example, butane (CH3CH2CH2CH3), propanal (CH3CH2CHO) and acetone (CH3SOSN3) have the same molecular mass of 58 and a boiling point in butane is 0 ° C, while for propanal it is 49 ° C, while acetone is56 ° C.The reason for the big difference lies in the fact that polar molecules have more opportunities to be attracted to each other than the non-polar molecules, so they must be more energy gap and therefore requires a higher temperature to melt the compounds or boiled.

With increasing molecular weight change physical properties of aldehydes.Formaldehyde (HCHO) is a gaseous substance at normal conditions, acetaldehyde (CH3CHO) boils at room temperature.Other aldehydes (except those from the high molecular weight) under normal conditions are liquids.Polar molecules are not easily mixed with nonpolar, because the polar molecules are attracted to each other, and nonpolar not able to squeeze between them.Therefore the hydrocarbons are not soluble in water, since the water molecules are polar.Aldehydes molecules of carbon number less than 5, are dissolved in water, but if the number of carbon atoms greater than 5, dissolution occurs.Good solubility aldehydes of low molecular weight due to the formation of hydrogen bonds between the hydrogen atom of the water molecule and oxygen atom of the carbonyl group.

polar molecules, formed by different atoms, can be quantitatively expressed by a number, called a dipole moment.Molecules formed identical atoms are not polar and have a dipole moment.The vector dipole moment is directed towards the element standing in the periodic table (for one period) to the right.If the molecule is composed of atoms of one subgroup, the electron density will be shifted to the side member with a smaller sequence number.Most of the hydrocarbons have a dipole moment or its magnitude is extremely small, but it is much higher aldehydes, which also explains the physical properties of aldehydes.