The major product obtained when 1-chlorobutane is treated with sodium ethoxide in ethanol is 1-butene. This reaction is an example of an elimination reaction, specifically E2 elimination.The reason for the formation of 1-butene predominantly is due to the strong base, sodium ethoxide NaOEt , which is present in the reaction. Sodium ethoxide is an alkoxide ion RO- derived from ethanol EtOH . In this reaction, the ethoxide ion acts as a base and abstracts a -hydrogen from the 1-chlorobutane molecule. The -hydrogen is the hydrogen atom on the carbon adjacent to the carbon attached to the chlorine atom.The E2 elimination mechanism involves a concerted process, where the ethoxide ion abstracts the -hydrogen, and the electrons from the C-H bond form a double bond between the - and -carbon atoms. Simultaneously, the C-Cl bond breaks, and the electrons from the bond go to the chlorine atom, forming a chloride ion Cl- . This leads to the formation of 1-butene as the major product.The E2 elimination is favored in this reaction due to the strong, sterically unhindered base ethoxide ion and the primary alkyl halide 1-chlorobutane . The reaction conditions promote the elimination pathway over other possible substitution reactions like SN2 .