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110 CHEMISTRY ome of the other e am les of resonan e stru tures are ro ided by the carbonate ion and the carbon dioxide molecule. Problem 4.3 Fig. 4.5 Resonance in CO m2lecule, I, II 2– and III represent the three canonical lain the stru ture of ion in forms. terms of resonance. Solution In general, it may be stated that he single ewis stru ture based on • esonan e stabili es the mole ule as the the presence of two single bonds and energy of the resonance hybrid is less one double bond between carbon than the energy of any single cannonical and o ygen atoms is inadequate to structure; and, represent the molecule accurately as it represents unequal bonds. According • esonan e a erages the bond to the e erimental findings all arbon characteristics as a whole. 2– hus the energy of the resonance to o ygen bonds in are equi alent herefore the arbonate ion is best hybrid is lower than either of the two described as a resonance hybrid of the annoni al froms I and II ig canonicalformsI,II,andIIIshownbelow. Many misconceptions are associated with resonance and the same need to be dispelled. You should remember that : • he annoni al forms ha e no real e isten e • hemole uledoesnote istfora ertain fraction of time in one cannonical form and for other fractions of time in other 2– Fig. 4.4 Resonance in CO3, I, II and III cannonical forms. represent the three canonical • here is no su h equilibrium between forms. the annoni al forms as we ha e Problem 4.4 between tautomeri forms keto and lain the stru ture of 2 molecule. enol in tautomerism • he mole ule as su h has a single Solution structure which is the resonance he e erimentally determined arbon hybrid of the cannonical forms and which cannot as such be depicted by to o ygen bond length in 2 is m he lengths of a normal a single ewis stru ture arbon to o ygen double bond and arbon to o ygen tri le bond ≡ 4.3.6 Polarity of Bonds are m and m res e ti ely he arbon o ygen bond lengths in he e isten e of a hundred er ent ioni or CO m lie between the alues o alent bond re resents an ideal situation 2 In reality no bond or a compound is either for C=O and C≡ b iously a single ewis stru ture annot de i t this om letely o alent or ioni en in ase of position and it becomes necessary to o alent bond between two hydrogen atoms write more than one ewis stru tures there is some ionic character. and to consider that the structure of CO is best described as a hybrid of hen o alent bond is formed between 2 two similar atoms for e am le in , O , the canonical or resonance forms I, II Cl or F , the shared pair of electrons is and III. 2 2 2 equally attracted by the two atoms. As a result Reprint 2026-27