page 14 Flashcards
Polarity of the C-X Bond:
The electronegative halogen atom in alkyl halides creates a polar carbon-halogen (C-X) bond.
The halogen (
X) pulls electron density toward itself, making:
The carbon atom electron-deficient (
δ+
, electrophilic site).
The halogen atom electron-rich (
δ−).
Electrostatic Potential Maps:
Visualize the distribution of electron density:
Red regions indicate electron-rich areas (negative potential, halogen).
Blue regions indicate electron-deficient areas (positive potential, carbon).
Reactivity of the Electrophilic Carbon:
The electron-deficient carbon is the key site for nucleophilic attack in substitution reactions (e.g.,
SN1,
SN2).
Increasing Polarizability of Halogens:
As the size of the halogen increases (
F<Cl<Br<I):
The bond becomes longer and weaker.
The halogen becomes more polarizable, enhancing reactivity in nucleophilic substitution reactions.
Why is the carbon atom in alkyl halides electron-deficient?
Answer: The halogen’s electronegativity pulls electron density away from the carbon, leaving it with a partial positive charge (δ+).
What type of bond exists between carbon and halogen in alkyl halides?
Answer: A polar covalent bond.
Why is the electron-deficient carbon important in alkyl halides?
Answer: It is the site of nucleophilic attack in substitution reactions.
On an electrostatic potential map, what does the red region represent?
Answer: Electron-rich areas, such as the halogen atom (δ−).
How does the size of the halogen affect the polarizability of the C-X bond?
Answer: Larger halogens (
F<Cl<Br<I) are more polarizable, making the bond longer and weaker.
Which alkyl halide is more reactive in nucleophilic substitution:
CH3F or
CH3I?
Answer:
CH3I, because iodine is larger and more polarizable, making the bond weaker and more reactive.
