Química Orgánica 1 · Reacciones radicalarias y selectividad
Chloroethane from ethane and chlorine
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 hydrogen from ethane
A chlorine radical removes one of the six equivalent hydrogens, giving HCl and the ethyl radical. This step is exothermic for chlorine, so it is fast and not very selective, but here every hydrogen gives the same radical.
Las flechas curvas
- The unpaired electron on the chlorine radical supplies one electron of the new bond to hydrogen.
- One electron of the carbon–H bond pairs with it to complete the new bond to hydrogen.
- The other carbon–H electron stays behind as the unpaired electron of the new radical.
How many monochlorides?
Equivalent hydrogens give the same radical and therefore the same product; count distinct hydrogen environments to count monohalogenation products.
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 carbon 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.
Chloroethane and HCl
The ethyl radical took a chlorine atom from Cl2, giving chloroethane and a fresh chlorine radical that continues the chain.
Qué vas a practicar
Draw Cl–Cl homolysis and the two propagation steps that convert ethane into chloroethane.
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