KEY CONCEPT
Induction is the distribution of charge across σ bonds. Conjugation and resonance are much
more powerful effects and occur in systems with alternating single and multiple bonds.This type of electron sharing makes for very stable compounds because these compounds have
multiple resonance structures. This characteristic allows for the stabilization of a positive charge
once the nucleophile has bonded, making these compounds more susceptible to nucleophilic
attack.
STRAIN IN CYCLIC DERIVATIVES
Lactams and lactones are cyclic amides and esters, respectively. Certain lactams and lactones are
more reactive to hydrolysis because they contain more strain. β-lactams, for example, are four-
membered cyclic amides and are highly reactive due to significant ring strain; four-membered rings
have both torsional strain from eclipsing interactions and angle strain from compressing the normal
sp^3 angle of 109.5°. These molecules are part of the core structure of several antibiotic families, as
shown in Figure 9.12. The ring strain, and therefore the reactivity, is increased by fusion to a second
ring. The four-membered structure of a β-lactam also forces a trigonal pyramidal bond geometry on
the nitrogen atom in the ring, which reduces resonance, making hydrolysis more likely.
Figure 9.12. Penicillin, a β-Lactam-Containing AntibioticREAL WORLD
Many antibiotic families contain β-lactams, including the penicillin family, cephalosporins,
carbapenems, and monobactams. Many bacteria have developed β-lactamases, which break