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. For polyenes with more than 4 conjugated double bonds, the Fieser-Kuhn rules must be applied.  In 1959, Louis Frederick Fieser modified these rules with more experimental data, and the modified rule is known as the Holzward-Fischer rule. The rules base the prediction on the type of chromophores present, substituents on chromophores and changes due to the solvent.   Examples are conjugated carbonyl compounds, conjugated dienes, and polyenes.  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]  Examples are conjugated carbonyl compounds,   conjugated dienes, and polyenes.
  Woodward`s rules are a set of rules about how organic chemical compounds absorb ultraviolet light. Using these rules, the maximum UV absorption can be predicted, for example in these two compounds: These rules predict the maximum UV absorption of compounds. Here are two examples: They provide information about 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. (III) AROMATIC COMPOUNDS: 1) Basic value: for (a) ArCOR = 246 nm C. Endocyclic double bond: – Double bond present in a ring. For more standard and quality questions, you can α to our test suite program for GPAT, NIPER JEE, Pharmacist Recruitment Exam, Drug Inspector Recruitment Exam, PhD Entrance Exam for Pharmacy II), β UNSATURATED CARBONYL COMPOUNDS OR KETONES: 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 A. ring-shaped diene Homo: cyclic diene with conjugated double bond in the same ring. 2) Alkyl group or cyclic radical in ortho- and meta position = 3 nm. λmax = baseline + ∑substituent- contributes + ∑ other to it Each alkyl, cyclic radical or cyclic residue substitution: – 5 nm D. Exocyclic double bond: – Double bond in which one of the double bond atoms is part of a ring.
4) Polar groups: a) –OH, –OCH3, –OAlkyl in o, position m = 7 nm. E. Expanding double bond:– if there are more than conjugate double bonds. The acyclic conjugated diene or ring-shaped heterocyclic conjugated diene has a wavelength of 215 nm. 1. Holzward–Fieser rule for diene and conjugated polyenes. In 1945, Robert Burns gave the wood department a specific rule for correlating λmax with molecular structure. Basic value: – Each type of diene or trian system has a certain fixed value at which absorption takes place, this value is called the base value.
Take the online pharmacist test FREE: CLICK HERE. 2. Alkyl substituent or cyclic residue in position α = 10 nm According to the Holzward-Fischer rule, the λmax of the molecule can be calculated with a formula: – 1. Basic value: (a) acyclic α, β unsaturated ketones = 214 nm.
Comments are closed.