Physical & Chemical Properties Of Alkynes

Alkynes are unsaturated hydrocarbons which consist of at least one triple bond between carbon atoms. There are two types of alkynes: terminal and internal.  Terminal alkynes are triple-bonded compounds in which a carbon atom shares the triple bond with the carbon at the end of the chain. Internal alkynes are compounds in which the triple bond is between two carbon atoms, none of which are terminal. The general molecular formula of alkynes is CnH2n-2. The physical properties of alkynes are very similar to the physical properties of alkenes.

The uniqueness in the alkyne structure is due to the hybridization. The acidity of alkynes, non-polar bonding strength, and linearity are due to the triple bonds in these compounds. These compounds are slightly soluble in polar solvents and are totally insoluble in water. Alkynes have the capability of dissolving in organic solvents as the density of the solution is less, which is a characteristic feature of alkenes as well. For example, it has the capability to dissolve in ether solution.

These triple bonded compounds have a boiling point slightly higher than alkanes and alkenes. For example, The boiling point of Ethane is -88.6 C while Ethene is -103.7 C and Ethyne has a boiling point of -84 C. The boiling point increases with the increase in the number of carbon atoms.

The acidity of these triple bonded compounds is greater than their counterparts i.e. alkanes and alkenes. The sp hybridized alkynes are the most acidic. It can be deprotonated only by using strong bases. For example, ethane has a pKa value of 50 which makes it the least acidic, while ethene has a pKa value of 44 and ethyne is the most acidic with a pKa value of 25.

Due to the repulsion of electrons, they are relatively unstable compounds having high energy. The amount of energy present in the alkyne molecules is responsible for the evolution of a large amount of heat.

Er. Neeraj K.Anand is a freelance mentor and writer who specializes in Engineering & Science subjects. Neeraj Anand received a B.Tech degree in Electronics and Communication Engineering from N.I.T Warangal & M.Tech Post Graduation from IETE, New Delhi. He has over 30 years of teaching experience and serves as the Head of Department of ANAND CLASSES. He concentrated all his energy and experiences in academics and subsequently grew up as one of the best mentors in the country for students aspiring for success in competitive examinations. In parallel, he started a Technical Publication "ANAND TECHNICAL PUBLISHERS" in 2002 and Educational Newspaper "NATIONAL EDUCATION NEWS" in 2014 at Jalandhar. Now he is a Director of leading publication "ANAND TECHNICAL PUBLISHERS", "ANAND CLASSES" and "NATIONAL EDUCATION NEWS". He has published more than hundred books in the field of Physics, Mathematics, Computers and Information Technology. Besides this he has written many books to help students prepare for IIT-JEE and AIPMT entrance exams. He is an executive member of the IEEE (Institute of Electrical & Electronics Engineers. USA) and honorary member of many Indian scientific societies such as Institution of Electronics & Telecommunication Engineers, Aeronautical Society of India, Bioinformatics Institute of India, Institution of Engineers. He has got award from American Biographical Institute Board of International Research in the year 2005.