-I effect NF3+ > NR+ > NH3+ > NO2 > - C ≡ N (cyanide group) > - CHO (aldehyde) > -RC (= O) R’ > - R - COOH > F > Cl > Br > I > - O - R > - O H > - C ≡ CH > - NH2 ⋍ ⏣ > CH = CH2 > H

+I effect CHΘ > NHΘ> OΘ> O > -COO > - C(CH3)3 > - H - C - (CH3)2 > -CH2 - CH3 > - CH3

sirf sigma bond me hi dikhhta hai. ye distance dependent hai. inversly propotional

RULES OF STABILITY OF RESONATING STUCTURE

+M effect -CH2 –NH, –NH2,–NHR, –NR2, – O, – OH, –OR, – F, – Cl, –O–COR, – NHCOR, –SH, – SR etc.

The group which shows the –M effect includes –NO2, –CN, –COX, –SO3H, – CHO, –CONH2, –COR, –COOH, –COOR etc.

The following important points must be remembered: The resonance structures are the hypothetical structures of the conjugated compounds which are used to explain the movement of electrons. The actual structure of the conjugated compound is a resultant hybrid of all the resonating structures. This phenomenon is known as delocalisation, mesomerism or resonance.

Conditions for Resonance 1. If there is a conjugation of two pi-bonds (means two pi-bonds alternately), then electrons of one pi-bond would be transferred to the other bond. (According to I–effect) Resonance Structure - Conjugation of two pi-bonds 2. If there is a conjugation of one negative charge or a lone pair electron and one pi-bond (pi- sigma- lone pair/ electron), then the electrons or a lone pair electrons are transferred towards the pi-bond. 3. If there is a conjugation of the pi bond and one positive charge (pi- sigma- +ve charge), then electrons of the pi-bond are transferred towards the positive charge. 4. If there is a conjugation of free radical and one pi bond (pi- sigma- free radical). 5. If there is a conjugation of one lone pair or negative charge and one positive charge (lone pair-sigma- +ve charge), then the lone pair electrons or negative charge are transferred towards the positive charge.

The bulky group attached at the ortho position then due to crowding factor resonance of benzene ring with bulky group gets disrupted. Applied for bulky like cooh, no2, nme2, ect it is not applied for smaller grouos like F, CN, OME, NH2, D, OH, ETC

triple bond < double bond < single bond.

Applications of Mesomeric Effect Carbocation Stability Carbocation’s stability is enhanced by resonance. All the aromatic compounds are always more stable as compared to non-aromatic compounds due to the effect of resonance. Stability of Carbanion (a) Carbanion’s stability is increased by resonance. Stability of Free Radicals (a) Resonance increases the stability of free radicals.

COMPARISON OF ENERGY 1.check aromaticity 2.more resonance 3.equivalent resonance 4.conjugation- extended and cross. extended is more stable. 5 check overlapping. 6. check donor atom.

Compound which have more benzene like stru. is more stableee...

All aliphatic compounds are non-aromatic. A few examples of non-aromatic compounds are as follows:1-hexyne,1-Neptune,1-octyne,1-online,1, 4-cyclohexadiene,1, 3, 5-cycloheptatriene,4-vinyl cyclohexene,1, 5, 9-cyclo deca triene.

Antiaromatic Compounds Are Unusually Unstable What are the key factors that determine whether a molecule is antiaromatic? It is similar to the requirements for aromaticity, except for one key factor (in red). The molecule must be cyclic The molecule must be conjugated all the way around the ring The molecule must be flat The molecule must have (4, 8, 12, 16…) pi electrons (summarized algebraically as “4n where n is a natural number”). Contrast this with aromatic molecules, which must have (2, 6, 10, 14, 18…) pi electrons. Anti-aromatic molecules are unusually unstable.

The aromatic compounds are always cyclic structures. Each element of the ring within the structure must and should have a p-orbital ring which is in a perpendicular form to the ring, and this makes it a planar molecule All the compounds obey Huckel’s Rule, i.e all the aromatic compounds should have the (4n+2) Pi number of electrons. The last one is that the organic compound has to be flat.

At ortho and para position e- density increases due to +M effect & decreases due to -M effect.At méta position there is no mesomeric effect.

Things to Remember The Ortho effect is the process in which the basic strength decreases with electron-withdrawing or electron releasing groups in the ortho position. The ortho-substituted anilines are weaker bases than aniline irrespective of the electron-withdrawing or electron releasing nature. The acidic property of a compound in which a group is at the ortho position to the carboxyl group is more than the benzoic acid. o-anisidine is a weaker base than aniline because of the ortho effect. The relative basic strength of Nitroanilines is of the order: aniline > m-nitroaniline > p-nitroaniline > o-nitroaniline.

Rotation single bond me zyada hota hai, jiska jitna single bond character utna rortation. double bond me bond tutt jata hai, usme rortaion zyada aasani se hoga to rotation energy barrier kam ho javega. aromatic ya anti aro dekh lena hai, agar ek stru aro or other anti aaya to rotation energy and bond length aromatic wale ki zyada hogi and rotation energy barrier antiaro ki zyada hogi.

Hyperconjugation effect is a permanent effect in which localization of σ electrons of C-H bond of an alkyl group directly attached to an atom of the unsaturated system or to an atom with an unshared p orbital takes place.

Greater the number of alkyl groups attached to the carbon atom, the greater the hyper conjugation.

stability directly propotional to alpha hydrogens.

According to Bredt's rule, a bicyclic molecule having bridge, bridge C cannot be sp2 hybridised. Therefore, a double bond cannot be formed at the bridgehead.

Inductive Effect on Acidity and Basicity Using the inductive effect, we can predict the acidity and basicity of compounds. As a generalisation, it may be said that the electron-withdrawing groups (EWG) increase the acidity of a compound, and the electron-donating group decrease the acidity of a compound. This is because, if we take the conjugate base of the acid, that is, RCOO-, if R is electron-withdrawing, then the conjugate base is stabilised via delocalisation of the formed negative charge. If R had been electron-donating, then the conjugate base would have been destabilised because of inter-electronic repulsions

1.neutral compound will be more stable...... 2. resonating structure which have octate of each complete atom is more stable . jiske uppar charge hai •sirf usi ka octet check karna hai....... 3] resonating stru. having more π bond is more stable........... 4] negativecharge on more electronegative atom is stable while positive charge on less ve electronegative atom........ 5]same like charges as far as possible [due-dur] opp. unlike charge: as as possible [pas-pas]