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Is the lone pair on the N atom on a cyanine dye count as a pi e pair?

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AussieKenDoll:
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!

mjc123:
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.

AussieKenDoll:
so the total lone pairs are 3+K right?

mjc123:
Total pi pairs

hollytara:
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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