Woodward Rules for Conjugated Dienes

A Woodward-Fieser set of rules for servants is listed in Table 1. A diene is either homoannular with the two double bonds contained in a ring, or heteroannular with two double bonds distributed between two rings. In 1959, Louis Frederick Fieser modified these rules with more experimental data and the modified rule is known as the Holzward-Fischer rule. 1. Holzward–Fieser rule for conjugated diene and polyenes. Woodward`s rules are a set of rules about how organic chemical compounds absorb ultraviolet light. E. Expanding double bond:– if there are more than conjugated double bonds. The acyclic conjugated diene or ring-shaped heterocyclic conjugated diene has a wavelength of 215 nm. For polyenes with more than 4 conjugated double bonds, the Fieser-Kuhn rules must be applied. [3] Woodward`s rules, named after Robert Burns Woodward and also known as Woodward–Fieser rules (for Louis Fieser), are several sets of empirically derived rules that attempt to predict the wavelength of the maximum absorption (λmax) in an ultraviolet-visible spectrum of a given compound.

The inputs used in the calculation are the type of chromophores present, auxochromes (substituents on chromophores) and solvents. [ 1] [2] Examples are conjugated carbonyl compounds,[3] [4] [5] conjugated dienes,[3][6] and polyenes. [3] [5] They provide information on the wavelength of the maximum absorption (symbol λmax) in an ultraviolet-visible (UV) spectrum of a compound. The rules are named after Robert Burns Woodward. He was a professor at Harvard University, which was awarded the Nobel Prize in Chemistry in 1965. The rules are sometimes called Woodward-Fieser rules to honor Louis Fieser. One. Ring-shaped diene homo: – cyclic diene with double conjugate bond in the same ring. These rules can be used to predict maximum UV absorption, for example in these two compounds:[8] The rules base the prediction on the type of chromophores present, substituents on chromophores and changes due to the solvent. [1] [2] Examples are conjugated carbonyl compounds,[3][4] conjugated dienes,[5] and polyenes. [4] III) AROMATIC COMPOUNDS: 1) Baseline: for a) ArCOR = 246 nm. 2.

Alkyl substituent or cyclic radical in position α = 10 nm. 4) Polar groups: a) –OH, –OCH3, –OAlkyl in o, position m = 7 nm. 1. Baseline: a) acyclic α, β unsaturated ketones = 214 nm For more standard and quality questions, you can join our GPAT, NIPER JEE Test Series Program, Pharmacist Recruitment Exam, Drug Inspector Recruitment Exam, PhD Pharmacy Entrance Exam II) α, β UNSATURATED CARBONYL COMPOUNDS OR KETONES: According to the Holzward-Fischer rule, the λmax of the molecule can be calculated using a formula: Any alkyl substitution, ring residue or ring residue: – 5 nm Take part in the free online pharmacist test: Click here Basic value: – Each type of diene or triene system has a certain fixed value at which absorption takes place, this value is called the base value. D. Exocyclic double bond: double bond in which one of the double bond atoms is part of a ring. In 1945, Robert Burns gave the wood department a specific rule for correlating λmax with molecular structure. 2) alkyl group or cyclic radical in ortho- and meta position = 3 nm. In the compound on the left, the base value is 214 nm (a heteroanne-shaped diene).

This group of services has 4 alkyl substituents (labeled with 1,2,3,4) and the double bond in one ring is exocyclic to the other (addition of 5 nm for an exocyclic double bond). In the compound on the right, diene is homoannular with 4 alkyl substituents. The two double bonds in the central ring B are exocyclic with respect to rings A and C. e) α, β unsaturated carboxylic acids and esters = 195 nm λmax = base + ∑substituent- contributes + ∑ other contributes to C. Endocyclic double bond: – Double bond present in a ring.