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Topic: distance between two central carbons  (Read 9791 times)

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studygirl

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distance between two central carbons
« on: July 04, 2005, 10:10:19 PM »
The structure of 1,3 butadiene is usually written as H2C(double bond)(double bond)CH-CH(DOUBLE BOND )(DOUBLE BOND)CH2

THE AVERAGE BOND LENGTHS GIVEN IN TABLE 9.2 IN YOUR TEXTBOOK ARE C-C OF 154PM AND C(DOUBLE BOND)(DOUBLE BOND)C OF 133pm. Explain the fact that the observed value of the distance between the two central carbon atoms in 1,3 butadiene is 146pm.

i am not sure what the question is, or how to approach, can someone explain this question to me, plz. thanks
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Benzene265

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Re:distance between two central carbons
« Reply #1 on: July 04, 2005, 10:20:35 PM »
Look up resonance.
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Offline Winga

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Re:distance between two central carbons
« Reply #2 on: July 05, 2005, 07:51:22 AM »
Another question:

Is it the bond length between 2nd & 3rd carbons is slightly longer than 1,2 or 3,4 carbons's?
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Offline Mitch

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Re:distance between two central carbons
« Reply #3 on: July 05, 2005, 04:41:40 PM »
Quote from: Winga on July 05, 2005, 07:51:22 AM
Another question:

Is it the bond length between 2nd & 3rd carbons is slightly longer than 1,2 or 3,4 carbons's?

Probably.
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Offline Winga

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Re:distance between two central carbons
« Reply #4 on: July 06, 2005, 12:50:04 AM »
MOs of butadiene:

pi2


pi1
« Last Edit: July 06, 2005, 12:52:54 AM by Winga »
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Offline Winga

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Re:distance between two central carbons
« Reply #5 on: July 06, 2005, 12:57:44 AM »
The reason is in the pi2 orbital, the e- density is localised between 1 and 2 carbons & 3 and 4 carbons.
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Offline Mitch

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Re:distance between two central carbons
« Reply #6 on: July 06, 2005, 02:12:53 AM »
Quote from: Winga on July 06, 2005, 12:57:44 AM
The reason is in the pi2 orbital, the e- density is localised between 1 and 2 carbons & 3 and 4 carbons.

Sounds good.
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Offline AWK

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Re:distance between two central carbons
« Reply #7 on: July 06, 2005, 02:57:24 AM »
trans-1,3-butadiene
C=C 134.5 pm, C-C 146.5 pm , angle 123.3 deg in gas phase
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