Slides6 - Chapter 6 ALKENES: STRUCTURE AND REACTIVITY...

Info iconThis preview shows pages 1–5. Sign up to view the full content.

View Full Document Right Arrow Icon
Chapter 6 ALKENES: STRUCTURE AND REACTIVITY
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
INDUSTRIAL PREPARATION OF ALKENES Alkenes (or olefins) are hydrocarbons (C,H) that contain a C=C double bond. H C C H H H H C C H CH 3 H Ethene (Ethylene) Propene (Propylene) 26 million tons per year 14 million tons per year H C C C C H H H H H H H H H 2 H C C H H H + H H D (C-C) = 376 kJ/mol D (C-H) = 438 kJ/mol D ( π C=C) = 281 kJ/mol D (H-H) = 436 kJ/mol Δ H o = + 376 + 2(438) - 2(281) - 436 = + 254 kJ/mol but Δ S o is positive and T is high that makes T Δ S o > Δ H o and therefore Δ G o = Δ H o - T Δ S o < 0 Thermal cracking is an example of a reaction whose energetics are dominated by entropy ( Δ S o ) rather than by enthalpie ( Δ H o ). H C C H H H H 2 900 o C
Background image of page 2
MOLECULE'S DEGREE OF UNSATURATION Because of double bonds, alkenes have fewer H than alkanes with the same number of C, and are therefore referred as unsaturated. Each double bond corresponds to a loss of 2 H from the alkane formula C n H 2n+2 Each ring corresponds to a loss of 2 H from the alkane formula C n H 2n+2 butene C 4 H 8 H 2 C CH CH 2 CH 3 H 2 C H 2 C CH 2 CH 2 cyclobutane C 4 H 8 H 2 C CH CH CH 2 butadiene C 4 H 6 HC H 2 C CH 2 CH cyclobutene C 4 H 6 HC HC CH CH cyclobutadiene C 4 H 4 H 2 C HC CH 2 CH bicyclobutane C 4 H 6 DOU = 0 DOU = 1 DOU = 1 DOU = 2 DOU = 2 DOU = 2 DOU = 3 H 3 C CH 2 CH 2 butane C 4 H 10 CH 3
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Number of rings DEGREE OF UNSATURATION OF MOLECULES CONTAINING OTHER ELEMENTS THAN C AND H ! Add the number of halogens ( F , Cl , Br ) to the number of H. Ignore the number of oxygens. Substract the number of nitrogens from the number of H. saturated C n H 2n+2 1 unsaturation C n H 2n 2 unsaturations C n H 2n -2 H 2 C CH CH Br CH 2 Br C 4 H 6 Br 2 C 4 H 6 H 2 H 2 C CH CH H CH 2 H C 4 H 8 = C n H 2n 1 unsaturation HC H 2 C CH 2 C O H C 4 H 6 O HC H 2 C CH 2 C H C 4 H 6 C n H 2n -2 2 unsaturations C 4 H 7 N
Background image of page 4
Image of page 5
This is the end of the preview. Sign up to access the rest of the document.

This document was uploaded on 02/03/2011.

Page1 / 17

Slides6 - Chapter 6 ALKENES: STRUCTURE AND REACTIVITY...

This preview shows document pages 1 - 5. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online