C effects are generally stronger than I effects. C effects can be effective over much longer distances than I effects – provided that conjugation is present. I effects are determined by distance, C effects are determined by relative positions. | ORGANIC CHEMISTRY Dr Nam T. S. Phan Faculty of Chemical Engineering HCMC University of Technology Office: room 211, B2 Building Phone: 8647256 ext. 5681 Email: ptsnam@ Chapter 2: ELECTRONIC & STERIC EFFECTS Conjugation / Mesomeric Steric Electronic Inductive Hyperconjugation Effects INDUCTIVE EFFECTS (I) C-C s bond in butane: almost completely nonpolar C-C s bond in 1-fluorobutane: polarized C1 is more positive than C2 as a result of electron-attracting ability of F The more electronegative the X, the stronger the –I effect The more electropositive the Z, the stronger the +I effect -I -I Through a period in a periodic table Through a group in a periodic table CH3CH2CH2COOH CH3CH2CH(Cl)COOH 139 CH3CH(Cl)CH2COOH ClCH2CH2CH2COOH Strong -I weak -I CONJUGATION / MESOMERIC EFFECTS (C / M) Electron delocalization in a conjugated system: Alternating single & multiple bonds O is more electronegative than C Electrons move through . | ORGANIC CHEMISTRY Dr Nam T. S. Phan Faculty of Chemical Engineering HCMC University of Technology Office: room 211, B2 Building Phone: 8647256 ext. 5681 Email: ptsnam@ Chapter 2: ELECTRONIC & STERIC EFFECTS Conjugation / Mesomeric Steric Electronic Inductive Hyperconjugation Effects INDUCTIVE EFFECTS (I) C-C s bond in butane: almost completely nonpolar C-C s bond in 1-fluorobutane: polarized C1 is more positive than C2 as a result of electron-attracting ability of F The more electronegative the X, the stronger the –I effect The more electropositive the Z, the stronger the +I effect -I -I Through a period in a periodic table Through a group in a periodic table CH3CH2CH2COOH CH3CH2CH(Cl)COOH 139 CH3CH(Cl)CH2COOH ClCH2CH2CH2COOH Strong -I weak -I CONJUGATION / MESOMERIC EFFECTS (C / M) Electron delocalization in a conjugated system: Alternating single & multiple bonds O is more electronegative than C Electrons move through p-bond network towards C=O The conjugated system is polarized C=O has negative conjugation / mesomeric effect (-C / -M) on the conjugated system +C -C +C -C +C -C +C -C -C +C +C -C -C +C -C groups generally contain an electronegative atom (s) or / and a p-bond (s): CHO, C(O)R, COOH, COOR, NO2, CN, aromatics, alkenes Cl, Br, OH, OR, SH, SR, NH2, NHR, NR2, aromatics, alkenes +C groups generally contain a lone pair of electrons or a p-bond (s): Aromatics or alkenes can be both +C and-C +C Through a period in a periodic table Through a group in a periodic table +C INDUCTIVE vs CONJUGATION EFFECTS Mobility of hydrogen atoms: almost the same -C INDUCTIVE vs CONJUGATION EFFECTS C effects are generally stronger than I effects C effects can be effective over much longer distances than I effects – provided that conjugation is present I effects are determined by distance, C effects are determined by relative positions HYPERCONJUGATION EFFECTS (H) Electron density from .
