Rep:Mod:HB2515Transitionstates5

Table 2: Lengths of the Carbon-Carbon bonds throughout the reaction (In Angstroms)

	Ethene	Butadiene	Transition state	Hexene	Change in bond length
C1-C2	1.327	-	1.382	1.535	Lengthens
C2-C3	-	-	2.114	1.537	-
C3-C4	-	1.333	1.380	1.501	Lengthens
C4-C5	-	1.471	1.411	1.337	Shortens
C5-C6	-	1.333	1.380	1.501	Lengthens
C6-C1	-	-	2.116	1.537	-

Table 3: Change in hybridisation of the carbon atoms

Carbon atom	Change in hybridisation
1	sp2 → sp3
2	sp2 → sp3
3	sp2 → sp3
4	no change
5	no change
6	sp2 → sp3

As it can be observed in Tables 2 and 3, as the bond gains sp³ character (only one sp³ carbons either side of the bond to two), the bond lengthens.

In this case, the C₄-C₅ remains with two sp² carbons either side, but the bond becomes shorter. This is due to the fact that the elctron dentiy was previously delocalised over multiples double bonds. Now that it is localised to that one bond, the bond is more electron rich and therefore becomes shorter (and stronger).

In the reaction state, the C₂-C₃ and C₆-C₁ have lengths inferior to two times the Van der Waal radius of the carbon atom (1.7 A). This porves that the carbon atoms are starting to interact in the transition state, before forming a single covalent bond in the product.

A typical C-C bond length is . A typical C=C bond length is . This is consistent with the lengths of the bonds in cyclohexene, but the single bond adjacent to the C=C bond are shortened from the electron density being slightly shortend due to higher electron density (again giving stronger bonds).