Química Orgánica 1 · Reacciones radicalarias y selectividad
Chlorocyclopentane from cyclopentane
Condiciones: Cl₂, hν
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Arrastra desde los electrones que se mueven hasta donde van, o toca uno y luego el otro. Cada flecha se revisa; Pista te ayuda cuando te atascas. No necesitas cuenta.
El mecanismo, paso a paso
Siguiente reproduce las flechas curvas de cada paso y las explica. Los pasos escritos están abajo.
Leer los 5 pasos escritos
Initiation: split Cl₂ with light
Light breaks the weak Cl–Cl bond homolytically: each chlorine atom keeps one of the two bonding electrons, giving two neutral chlorine radicals and no ions. A second Cl₂ molecule waits for the propagation steps.
Las flechas curvas
- One electron of the Cl–Cl bond stays on the first atom.
- The other electron of the Cl–Cl bond stays on the second atom, so the bond splits evenly into two radicals.
Propagation: abstract a ring hydrogen
The chlorine radical removes one ring hydrogen, giving HCl and the cyclopentyl radical. Because the ring is symmetric, every hydrogen is equivalent and leads to the same secondary radical.
Las flechas curvas
- The unpaired electron on the chlorine radical supplies one electron of the new bond to hydrogen.
- One electron of the ring C–H bond pairs with it to complete the new bond to hydrogen.
- The other ring C–H electron stays behind as the unpaired electron of the new radical.
Why chlorine is fine here
Chlorination is unselective, which usually gives mixtures; it is synthetically useful only when all hydrogens are equivalent, as in cyclopentane.
Propagation: take Cl from a second Cl₂
The carbon radical attacks Cl₂, forming the C–Cl bond and releasing a new chlorine radical. That radical starts the next cycle, so one initiation event drives many cycles.
Las flechas curvas
- The unpaired electron on ring C supplies one electron of the new bond to Cl.
- One electron of the Cl–Cl bond completes that new bond.
- The other Cl–Cl electron stays on the far Cl, regenerating the chain-carrying radical.
Chlorocyclopentane and HCl
The cyclopentyl radical took a chlorine atom from Cl2: chlorocyclopentane forms and a new chlorine radical carries the chain.
Qué vas a practicar
Draw the initiation and both propagation steps that turn cyclopentane into chlorocyclopentane.
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