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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: tony.hegyes on March 14, 2012, 06:41:53 AM

Title: Lycopene reaction with Br2 - water
Post by: tony.hegyes on March 14, 2012, 06:41:53 AM

Good day!

I have stumbled upon the following question: What happens when you add Br2 dissolved in CCl4 to lycopene (http://en.wikipedia.org/wiki/Lycopene)? The good answer was that it loses its colour.

Could someone explain to me please why so? And is this a general rule for all dyes?

Thank you!

Title: Re: Lycopene reaction with Br2 - water
Post by: sjb on March 14, 2012, 07:05:28 AM

Quote from: tony.hegyes on March 14, 2012, 06:41:53 AM

Good day!

I have stumbled upon the following question: What happens when you add Br2 dissolved in CCl4 to lycopene (http://en.wikipedia.org/wiki/Lycopene)? The good answer was that it loses its colour.

Could someone explain to me please why so? And is this a general rule for all dyes?

Thank you!

What functionality does lycopene have? Does this react in any way with bromine?

Title: Re: Lycopene reaction with Br2 - water
Post by: tony.hegyes on March 14, 2012, 07:19:39 AM

Yes, the two do react. Bromine atoms break a few pi-Bonds.

Title: Re: Lycopene reaction with Br2 - water
Post by: fledarmus on March 14, 2012, 07:25:16 AM

A molecule wouldn't appear colored unless it was absorbing radiation in a visible wavelength. What structure in lycopene can absorb visible light? How might this structure change if you add bromine?

This might help: http://homepages.gac.edu/~anienow/CHE-372/Labs/Conjugated%20Dyes.pdf (http://homepages.gac.edu/~anienow/CHE-372/Labs/Conjugated%20Dyes.pdf)

Title: Re: Lycopene reaction with Br2 - water
Post by: tony.hegyes on March 14, 2012, 07:30:08 AM

Thank you Fledarmus! It seems that lycopene loses its colour because of the missing pi-Bonds - the effect of bromium addition.

Title: Re: Lycopene reaction with Br2 - water
Post by: AWK on March 14, 2012, 09:18:18 AM

Bromine also loses its color!