Organic Chemistry: Functional Groups & Equations

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Questions and Answers

At a pH of 8.0, what is the percentage of the ionized form of the acid?

80%

100%

20%

50% (correct)

What is the pH level at which the ionized form of the acid is at 20%?

8.0

5.5

2.0

7.4 (correct)

At a pH of 5.5, what proportion of the acid is in the ionized form?

50%

0.3%

10%

99.7% (correct)

At what pH will an acid be completely in its unionized form (100%)?

2.0 Signup and view all the answers

When pH is increased from 5.5 to 7.4, how does the proportion of the ionized form change?

Increases to 80% Signup and view all the answers

If the pH is 8.0 and the concentration of the acid form is represented as [HA], what is the representation of the ionized form?

[A-] = 1 Signup and view all the answers

What is the total addition of [A-] and [HA] at a pH of 8.0?

2 Signup and view all the answers

At pH levels lower than 5.5, how does the ionized form behave?

Decreases significantly Signup and view all the answers

Which factor does not directly affect the acidity of a functional group?

Chirality Signup and view all the answers

What does the Henderson-Hasselbalch equation primarily describe?

The relationship between pH and ionization Signup and view all the answers

Which of the following describes the solubility effects of functional groups in drugs?

They influence both water and lipid solubility. Signup and view all the answers

In the context of functional groups, what is meant by steric effects?

The physical size and shape of molecules affecting reactivity Signup and view all the answers

What is the primary reason for drug chirality to be significant in medicinal chemistry?

It can lead to drugs having different biological activities. Signup and view all the answers

Which aspect of a functional group primarily influences its solubility in water?

Acid-base properties Signup and view all the answers

What is the effect of resonance on the properties of functional groups in medicinal chemistry?

It stabilizes the ionized form of weak acids. Signup and view all the answers

When considering acid-base properties, what would a higher pKa value imply about a weak acid?

It is less likely to ionize in solution. Signup and view all the answers

What term describes molecules with the same molecular formula but different spatial arrangements?

Stereoisomers Signup and view all the answers

Which type of stereoisomer consists of non-superimposable mirror images?

Enantiomers Signup and view all the answers

In R/S configuration, which step involves assigning priorities to the ligands?

Step 1 Signup and view all the answers

What is the lowest possible priority ligand in the R/S configuration method?

Hydrogen Signup and view all the answers

Which of the following statements is true regarding diastereomers?

They have more than one chiral center. Signup and view all the answers

In terms of geometric isomers, what does the E/Z nomenclature refer to?

Different arrangements of alkene substituents Signup and view all the answers

If the arrangement of ligands 1 to 3 is counterclockwise, what configuration should be assigned?

S Signup and view all the answers

Which of the following statements is correct about the enantiomer of Ibuprofen?

Only the S enantiomer has analgesic properties. Signup and view all the answers

What happens to Ecstasy in the alkaline environment of the small intestine?

It becomes nonpolar and diffuses into the blood. Signup and view all the answers

In the stomach, which type of drug is more likely to be absorbed?

Weak acids. Signup and view all the answers

What is the implication of a drug's pKa when the surrounding pH is above the pKa for acidic drugs?

The drug will mostly remain in the ionized form. Signup and view all the answers

How does chirality affect a molecule with 'n' asymmetric carbons?

It gives rise to 2n optical isomers. Signup and view all the answers

What determines whether weak bases are mostly ionized or un-ionized?

The pH relative to the pKa of the bases. Signup and view all the answers

In terms of electronic effects in drug molecules, which property is NOT typically considered?

Thermal conductivity. Signup and view all the answers

What is a primary characteristic of a chirality in molecules?

Orientation of functional groups in three-dimensional space. Signup and view all the answers

Which statement about drug molecules and their absorption is false?

Only nonpolar drugs can diffuse through lipid membranes. Signup and view all the answers

What is the correct stereochemical designation for a molecule with the priority order of substituents I > Br > F and H in the back?

S Signup and view all the answers

Which of the following best describes the relationship between enantiomers?

They have identical connections but differ in spatial orientation. Signup and view all the answers

What does the Easson-Stedman hypothesis suggest about interactions with receptors?

A minimum of three intermolecular interactions is required. Signup and view all the answers

If a drug exhibits dextrorotatory properties, how would this be denoted in optical rotation notation?

(+) Signup and view all the answers

In which scenario is a molecular compound considered achiral?

When all substituents can be superimposed. Signup and view all the answers

How is the relationship between optical rotation and R, S designation characterized?

They are unrelated aspects of stereochemistry. Signup and view all the answers

What characterizes a racemate in stereochemistry?

An equal mixture of two enantiomers. Signup and view all the answers

Which of the following statements is true regarding amino acids?

Amino acids are predominantly found in their L-form. Signup and view all the answers

Study Notes

Functional Groups (FG)

A specific part of a compound or drug that dictates the compound's behavior and properties, thereby influencing biological response
Chemical properties of FG:
- Electronic effects - Resonance and Inductive effect
- Steric Effects
- Acid-base properties
- Chirality
- Solubility Effects: Water and Lipid Solubility, Salt Formation

Henderson-Hasselbach equation

First described by Lawrence Henderson in 1908 and modified by Karl Hasselbach in 1916
Used to calculate the pH of a solution of a weak acid or weak base
Describes the relationship between the pH of a solution, the pKa of the acid (or base) and the ratio of the concentrations of the acidic (or basic) form and its conjugate base (or acid) form

3. Acid-Base Properties

Weak Acids: HA ↔ H+ + A-
- HA: Acid
- A-: Conjugate Base
- Equation: pKa = pH + log([acid]/[conjugate base])
Weak Bases: B:H ↔ H+ + B:
- B:H: Conjugated Acid (Protonated Form)
- B: Base (Unprotonated form)
- Equation: pH = pKa + log([base]/[conjugate acid])
- Equation: pH = pKa + log([un-ionized]/[ionized])

Importance of Ionization Example: Amobarbital

Calculation of % ionization of amobarbital at pH 2.0, pH 8.0, and pH 7.4
At pH 8.0, equal amounts of acid and conjugate base exist
At pH 7.4, ~20% of molecules are in the ionized form, leaving ~80% in the unionized form
At pH 5.5, the acid form predominates (~99.7% unionized)
At pH 2.0, amobarbital is in the unionized form (~100%)

General Rules for Ionization

Weak Acids:
- When pH < pKa, acids are more likely to be in the un-ionized (HA) form. The un-ionized form can diffuse through lipid membranes.
Weak Bases:
- When pH < pKa, bases are more likely to be in the ionized (BH+) form. The ionized form will not diffuse through a lipid membrane.

Absorption

Stomach (pH 2): Most acids will diffuse through the membrane (absorb), but bases will not.
Small Intestine (pH 4.8-8.2): Most acids will not absorb, but most bases will.

Chirality

Stereochemistry - The orientation of functional groups in three-dimensional space
Asymmetric carbon (chiral carbon) - a carbon atom bound to four different substituents
A molecule with "n" asymmetric carbons will have 2^n optical isomers
The spatial arrangement of a molecule affects its reactivity in chemical reactions, as well as its biological and physical properties.

Stereoisomers

Molecules with the same molecular formula but differing in the arrangement of their atoms in space
Different types: enantiomers, diastereomers, geometric isomers
Enantiomers: Non-superimposable mirror images of each other.
- Example: Ibuprofen - Only the S enantiomer has analgesic properties
Diastereomers: Non-superimposable, non-mirror images. Isomers with more than one chiral center.
Geometric isomers: E/Z alkene isomers - Diastereomers, which are a result of restricted rotation about a double bond

Absolute Configuration (R/S Convention)

Description of the order of ligands in space
R (rectus, right): Clockwise arrangement
S (sinister, left): Counterclockwise arrangement
Determined by the priority of the substituents around the stereogenic center. Higher atomic numbers indicate a higher priority

Easson-Stedman Hypothesis

Postulated that drug receptor interactions require at least three-point fit for optimal binding (minimum of 3 intermolecular interactions)
Explains why some enantiomers are more potent than others: The less potent enantiomer may interact with fewer sites on the receptor.

Optical Rotation & Key Points

Optical Rotation: Measure of the angle of rotation of plane-polarized light by a chiral compound
- (+) = d (dextrorotatory)
- (-) = l (levorotatory)
Optical rotation does not correlate to the R,S designation. The R and S designations are based on the spatial arrangement of the ligands and the R/S convention.
Enantiomeric: Not superimposable
Racemate: An equal mixture of two enantiomers
Amino acids: Chiral molecules (all L isomers)
Proteins: Chiral molecules - The interaction of chiral proteins (receptors) with different enantiomers of a chiral drug may involve different binding sites.

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Description

Explore the key concepts of functional groups and their impact on chemical behavior in this quiz. You'll also delve into the Henderson-Hasselbalch equation, crucial for understanding pH in weak acid and base solutions. Test your knowledge on acid-base properties and their applications.