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Chemistry Forums for Students => Organic Chemistry Forum => Organic Spectroscopy => Topic started by: Covfe₂ on October 01, 2017, 04:25:40 AM

Title: Woodward-Fieser Rules
Post by: Covfe₂ on October 01, 2017, 04:25:40 AM

Hey everyone.
I've just started an organic chemistry course and I'm struggling understanding the Woodward-Fieser Rules. Mainly I think it's with identifying the functional groups. I was hoping if someone could please confirm if my wavelength max was correct for my homework and any tips in general that would help.

(https://s25.postimg.org/66h98xepn/Compound1.png) (https://postimg.org/image/66h98xepn/)
Base value (Cyclopentenone)            =202
Double bond extending conjugation    = 30
Exocyclic double bond                      = 5
Alkyl substituents                           = (5 x 6) = 30


wavelength max                             = 267 nm


(https://s25.postimg.org/xh2kgvrx7/Compound2.png) (https://postimg.org/image/xh2kgvrx7/)

Base value (homoannular diene)        = 253
Double bond extending conjugation    = 30
Exocyclic double bond                     = (3 x 5) = 15
Alkyl substituents                           = (5 x 5) = 25


wavelength max                            = 323 nm


thank you!

Title: Re: Woodward-Fieser Rules
Post by: pgk on October 03, 2017, 11:24:45 AM

Yes, it is correct according Wikipedia.
But cross-check it, from spectroscopy textbooks because some authors give different values for alkyl substituents, whether being in α, β, γ or higher position from the carbonyl group.

Title: Re: Woodward-Fieser Rules
Post by: sjb on October 03, 2017, 04:36:09 PM

For the first isn't this a cyclohexenone? Can't remember how much difference this makes and my notes are a good distance away