Chemical Properties of Alkenes | Addition of Dihydrogen & Halogen

What are Alkenes

Alkenes consist of a large number of loosely held pi bonds. Due to the presence of such bonds they exhibit addition reactions. In addition reaction, the electrophiles (electron seeking species) are added to the double-bonded compounds which result in the formation of the additional product. Under special conditions, in some cases, it has the ability to undergo free radical substitution reactions also. Ozonolysis reaction and oxidation reaction are also prominently exhibited it.

Reactions of alkenes with different compounds

Addition of dihydrogen

Alkanes are formed on addition of one molecule of dihydrogen to alkenes in the presence of different types of catalysts such as palladium, nickel or platinum.

Addition of halogens

Vicinal dihalides are the products formed when alkenes react with halogens such as bromine, chlorine. Iodine is an exception as it does not exhibit addition reaction under normal conditions. Bromine solution loses its reddish-orange colour in carbon tetrachloride solution due to the addition of bromine to an unsaturated site. Hence this reaction is used as a test for the presence of unsaturation in a solution. The reaction of alkenes with halogens is an example of the electrophilic addition reaction.

Alkenes consist of a large number of loosely held pi bonds. Due to the presence of such bonds they exhibit addition reactions. In addition reaction, the electrophiles (electron seeking species) are added to the double-bonded compounds which result in the formation of the additional product. Under special conditions, in some cases, it has the ability to undergo free radical substitution reactions also. Ozonolysis reaction and oxidation reaction are also prominently exhibited it.

Addition of hydrogen halides

Alkyl halides are formed when hydrogen halides react with it. The reactivity exhibited by HI is more than HBr and the reactivity of HBr is more than HCl. The addition reaction is possible to both symmetrical and unsymmetrical alkenes. Addition reaction of hydrogen halides to unsymmetrical alkenes takes place in accordance with the following rules:

  • Markovnikov rule
  • Anti-Markovnikov rule

As per Markovnikov rule when unsymmetric alkene is added to hydrogen halide, halogen gets attached to the carbon having less number of hydrogen.

Alkenes consist of a large number of loosely held pi bonds. Due to the presence of such bonds they exhibit addition reactions. In addition reaction, the electrophiles (electron seeking species) are added to the double-bonded compounds which result in the formation of the additional product. Under special conditions, in some cases, it has the ability to undergo free radical substitution reactions also. Ozonolysis reaction and oxidation reaction are also prominently exhibited it.

As per anti-Markovnikov rule unsymmetric alkenes add hydrogen halide in the presence of peroxide.The reverse of Markovnikov rule occurs which results in the attachment of halogen to a carbon containing more number of hydrogens.

Alkenes consist of a large number of loosely held pi bonds. Due to the presence of such bonds they exhibit addition reactions. In addition reaction, the electrophiles (electron seeking species) are added to the double-bonded compounds which result in the formation of the additional product. Under special conditions, in some cases, it has the ability to undergo free radical substitution reactions also. Ozonolysis reaction and oxidation reaction are also prominently exhibited it.

Addition of water

It is made to react with water in the presence of few drops of sulphuric acid.This results in the formation of alcohols as per Markovnikov rule.

Alkenes consist of a large number of loosely held pi bonds. Due to the presence of such bonds they exhibit addition reactions. In addition reaction, the electrophiles (electron seeking species) are added to the double-bonded compounds which result in the formation of the additional product. Under special conditions, in some cases, it has the ability to undergo free radical substitution reactions also. Ozonolysis reaction and oxidation reaction are also prominently exhibited it.

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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.