Understanding Isomers, Alkynes, and Alcohols in Chemistry
Understanding Isomers, Alkynes, and Alcohols
Isomers are compounds that have the same condensed formula but differ in the way their atoms are arranged in the chain. Positional isomerism in alkenes is due to a change of position within the double bond chain.
Geometric isomerism, or cis-trans isomerism, occurs when the presence of a double bond prevents the free rotation of Carbon atoms. This results in different spatial arrangements, specifically cis (same side) and trans (opposite sides).
Optical isomerism, also known as stereoisomerism, occurs in compounds with the same bond order of atoms but different spatial arrangements.
Functional isomerism occurs when a condensed formula can belong to different functional groups.
Alkynes
Alkynes are unsaturated hydrocarbons with a triple bond (C≡C), also called acetylenic hydrocarbons. Their general formula is CnH2n-2. To name these compounds, use the same nomenclature as for alkenes, changing the ending “-ene” to “-yne”.
Arborescent Alkynes
The naming of arborescent alkynes follows the same rules as for arborescent alkenes.
Physical Properties of Alkynes
- The first three alkynes are gaseous at ambient temperature.
- Alkynes from C5 to C15 are liquids.
- Alkynes with 16 or more carbons are solid.
- Their melting and boiling points are higher than the corresponding alkenes.
- Density increases with increasing molecular weight.
Chemical Properties of Alkynes
Depending on the reaction conditions, alkynes can form alkenes or alkanes.
Methods of Obtaining Alkynes
- Through hydrolysis of calcium carbide.
- Dehydrohalogenation of dihalogenated compounds with a base.
Functional Groups: Halogenated Hydrocarbons
Halogenated hydrocarbons (F, Cl, Br, I) result from replacing one or more hydrogen atoms with one or more halogens. They can be classified as monohalogenated or polyhalogenated, depending on the number of halogens. Monohalogenated derivatives can be primary, secondary, or tertiary, depending on the carbon atom where the substitution occurs. Saturated monohalogenated derivatives are called alkyl halides.
To name primary alkyl halides, the halogen is named first, followed by the name of the corresponding hydrocarbon. For secondary and tertiary alkyl halides, the same procedure as for arborescent alkanes is followed. If two or more different halogens are present, they are named in the order I, Br, Cl, F.
Alkyl halides can react with an alcohol hydrazide. For example, Chloroethane (Ethyl chloride) is a liquid that turns into a gas at 12 degrees Celsius. It is colorless, has a slightly sweet flavor, and is used to manufacture tetraethyl lead, as a gasoline antiknock, as an anesthetic, as a coolant, to synthesize cellulose, as a fumigant, and to dissolve nitrogen, phosphorus, and fat.
Trichloromethane (chloroform) is a colorless liquid with a sweet, suffocating odor. It is freely soluble in alcohol and slightly soluble in water. It was historically used as an anesthetic.
Alcohols
Alcohols (R-OH) are formed when one or more hydrogen atoms are replaced by one or more hydroxyl groups. When only one hydrogen atom is replaced, alcohols can be primary, secondary, or tertiary. Alcohols can also be classified as monohydric, dihydric, trihydric, etc., depending on the number of hydroxyl groups.
To name primary alcohols, the name of the hydrocarbon is written with the ending “-ol”. When the hydroxyl group is at the end of the chain, it is considered to be attached to carbon number 1. Another way is to write the name “alcohol” followed by the name of the hydrocarbon with the ending “-ylic”. Another method is to consider the alcohol as a derivative of methanol (carbinol), such as “methyl carbinol”.
In secondary and tertiary alcohols, it is necessary to indicate the position of the hydroxyl radical.
Methanol (Methyl Alcohol)
Methanol is called wood alcohol because it is obtained from the distillation of wood. It is a colorless liquid with a pleasant odor when pure, less dense than water, and highly soluble. Methanol causes blindness and even death. It is used as a solvent in the manufacture of varnishes and paints, as fuel for cars, and as antifreeze.
Ethanol
Ethanol is obtained by the fermentation of certain sugars. It is used to make liqueurs, and the name given depends on the source of the sugar, such as Rum (sugarcane), Tequila (agave), Mezcal (maguey), Whiskey (barley), Vodka, and Brandy (juniper or grape).