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Topic: Is the lone pair on the N atom on a cyanine dye count as a pi e pair?  (Read 1166 times)

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Offline AussieKenDoll

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Is the lone pair on the N atom on a cyanine dye count as a pi e pair?
« on: October 17, 2019, 03:35:31 AM »
What is the total number of pi-electron pairs involved in the conjugation in the cyanine dye on the attached pic?
I got it as 2+K but its wrong according to the marking scheme, it shows as 3+K, so is the lone pair on the N atom on the cyanine dye count as a pi-e pair?

Below pic shows the resonance structure of a cyanine dye!
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Offline mjc123

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Re: Is the lone pair on the N atom on a cyanine dye count as a pi e pair?
« Reply #1 on: October 17, 2019, 05:10:23 AM »
Yes. Draw a curly arrow diagram to show how the two resonance structures interconvert, and you'll see that the N lone pair is involved in the delocalisation.
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Offline AussieKenDoll

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Re: Is the lone pair on the N atom on a cyanine dye count as a pi e pair?
« Reply #2 on: October 17, 2019, 05:57:37 AM »
so the total lone pairs are 3+K right?
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Offline mjc123

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Re: Is the lone pair on the N atom on a cyanine dye count as a pi e pair?
« Reply #3 on: October 17, 2019, 08:02:08 AM »
Total pi pairs
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Offline hollytara

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Re: Is the lone pair on the N atom on a cyanine dye count as a pi e pair?
« Reply #4 on: October 17, 2019, 10:34:05 AM »
Total pi pairs 3+K

If the N lone pairs in the resonance structures weren't part of the pi system, you would not be able to draw the other resonance structure!
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