page 31-35 Flashcards
What type of anions are solvated more strongly in polar protic solvents?
A: Smaller, more electronegative anions.
How does strong solvation affect nucleophilicity?
A: It shields the anion, making it less reactive.
In polar protic solvents, how does nucleophilicity change down a column of the periodic table?
A: Nucleophilicity increases as the size of the anion increases.
What is the relationship between nucleophilicity and basicity in polar protic solvents?
A: They are opposite; smaller anions are better bases but poorer nucleophiles.
Which halide ion is the strongest nucleophile in polar protic solvents?
A: I⁻ (iodide ion).
Why is I⁻ a better nucleophile than F⁻ in polar protic solvents?
A: I⁻ is less strongly solvated due to its larger size, making it more reactive.
Which halide ion is the weakest nucleophile in polar protic solvents?
A: F⁻ (fluoride ion).
What is the primary role of polar protic solvents in substitution reactions?
A: To solvate and stabilize ions, influencing nucleophilicity.
How does the size of an anion affect its solvation?
A: Larger anions are less strongly solvated, making them better nucleophiles.
What is the trend in nucleophilicity for halides (F⁻, Cl⁻, Br⁻, I⁻) in polar protic solvents?
A: I⁻ > Br⁻ > Cl⁻ > F⁻.
What does strong solvation of F⁻ in water result in?
A: Reduced nucleophilicity due to shielding by water molecules.
In polar protic solvents, why does basicity not directly correlate with nucleophilicity?
A: Solvent interactions reduce the reactivity of smaller, stronger bases.
What effect does the electronegativity of an anion have in polar protic solvents?
A: Higher electronegativity leads to stronger solvation, reducing nucleophilicity.
Which property of solvents makes them “polar protic”?
A: The ability to form hydrogen bonds.
How does methanol (CH₃OH) compare to water (H₂O) in solvating anions?
A: Methanol solvates less strongly than water due to fewer hydrogen bonding interactions.
What are polar aprotic solvents incapable of?
A: Hydrogen bonding.
What type of interactions do polar aprotic solvents exhibit?
A: Dipole-dipole interactions.
Name a common polar aprotic solvent with the formula CH₃COCH₃.
A: Acetone.
What is the common abbreviation for tetrahydrofuran?
A: THF.
Which polar aprotic solvent is represented by the structure HCON(CH₃)₂?
A: Dimethylformamide (DMF).
Why are polar aprotic solvents commonly used in substitution reactions?
A: They do not solvate nucleophiles strongly, allowing them to remain reactive.
What differentiates polar aprotic solvents from polar protic solvents?
A: Polar aprotic solvents lack O-H or N-H bonds and cannot form hydrogen bonds.
Which solvent among the following is polar aprotic: water, acetone, ethanol?
A: Acetone.
How do polar aprotic solvents interact with cations?
A: They stabilize cations through dipole-dipole interactions.
What is a key characteristic of all polar aprotic solvents?
A: They have a significant dipole moment but lack hydrogen bond donors.
Name two common applications of polar aprotic solvents.
A: Used in nucleophilic substitution reactions (e.g., SN2) and organometallic reactions.
What is a nucleophile?
A: A species that donates an electron pair to form a new covalent bond.
Give two examples of negatively charged oxygen nucleophiles.
A:
−OH (hydroxide) and
−OR (alkoxide).
Provide an example of a neutral oxygen nucleophile.
A:
H2O (water) or
ROH (alcohol).
What is a common nitrogen-based negatively charged nucleophile?
A:
N3−(azide).
Name a neutral nitrogen nucleophile.
A:
NH3 (ammonia) or
RNH2(amine).
Identify two examples of carbon-based negatively charged nucleophiles.
A:
−CN (cyanide) and
−C≡CH (acetylide).
What halogens act as negatively charged nucleophiles?
A:
C
l
−
Cl
−
,
B
r
−
Br
−
, and
I
−
I
−
.
Which sulfur species acts as a negatively charged nucleophile?
A:
−
H
S
−HS (hydrosulfide) and
−
R
S
−RS (thiolate).
Name a neutral sulfur nucleophile.
A:
H
2
S
H
2
S (hydrogen sulfide) or
R
S
H
RSH (thiol).
What type of nucleophiles are
C
H
3
C
O
O
−
CH
3
COO
−
(acetate)?
A: Negatively charged oxygen nucleophiles.
Which halide ion is the best nucleophile in polar protic solvents?
A:
I
−
I
−
(iodide).
What distinguishes a neutral nucleophile from a negatively charged one?
A: Neutral nucleophiles do not carry a formal negative charge.
Why are sulfur-based nucleophiles often stronger than oxygen-based nucleophiles?
A: Sulfur is less electronegative and more polarizable than oxygen, making it more nucleophilic.
Which negatively charged nucleophile is commonly used in organic synthesis to introduce a carbon-nitrogen triple bond?
A:
−
C
N
−CN (cyanide).
How do halogen nucleophiles like
C
l
−
Cl
−
,
B
r
−
Br
−
, and
I
−
I
−
behave in substitution reactions?
A: They act as good nucleophiles and displace leaving groups in nucleophilic substitution reactions.
