Medicinal Chemistry: Covalent Bonding Concepts

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Questions and Answers

What is the bond order of C-O bonds in CO32-?

4/3 (correct)

1.5

Which of the following statements about Lewis dot structures is true?

They show all possible resonance forms.

They work perfectly for all molecules.

They can explain the paramagnetism of O2.

They cannot accurately represent molecules with unpaired electrons. (correct)

What is a characteristic of isoelectronic species?

Same connectivity and same number of bonds (correct)

Different numbers of valence electrons

Different bond connectivity

Same number of total electrons

What connection does molecular orbital theory make regarding O2?

It confirms the existence of unpaired electrons in O2. Signup and view all the answers

How many valence electrons does carbon have?

4 Signup and view all the answers

When drawing a Lewis structure, which atom should you complete the octet for first?

The most electronegative atom Signup and view all the answers

Which of the following pairs are isoelectronic?

CO and NO+ Signup and view all the answers

What does the bond order of 2 signify?

It signifies a double bond is present. Signup and view all the answers

What is the first step in constructing a Lewis dot structure for a molecule?

Count the number of valence electrons on each atom Signup and view all the answers

Which of the following is a characteristic of free radicals?

They contain unpaired electrons Signup and view all the answers

What does the bond order represent in relation to a molecular bond?

The strength and length of the bond Signup and view all the answers

Which ion is NOT identified as a free radical?

Nitrogen ion Signup and view all the answers

In the process of arranging atoms for a Lewis dot structure, which atom is typically positioned at the center?

The atom with the lowest electronegativity Signup and view all the answers

What is the product of the reaction between nitric oxide and superoxide ion?

Peroxynitrite Signup and view all the answers

What type of reaction is a disproportionation reaction?

A reaction where one substance is oxidized and reduced simultaneously Signup and view all the answers

How many electrons can hydrogen accommodate when following the duet rule?

2 electrons Signup and view all the answers

Which process is associated with lowering blood pressure and involves a neurotransmitter?

Nitric Oxide (NO) Signup and view all the answers

What are the bond lengths for N≡O and N=O compounds respectively?

106 pm and 120 pm Signup and view all the answers

Which atoms can form multiple bonds?

C, N, O, P, S Signup and view all the answers

What is the bond order of the nitrogen-oxygen triple bond (N≡O)?

3 Signup and view all the answers

Which of the following is NOT a type of reactive oxygen species?

Nitric Oxide Signup and view all the answers

What is the first step in drawing the Lewis structure of a molecule?

Count the number of valence electrons on each atom Signup and view all the answers

In a Lewis structure, if the central atom has an incomplete octet, what is the appropriate action?

Form double or triple bonds using surrounding atoms' electrons Signup and view all the answers

What is the total number of valence electrons in the superoxide ion (O2^-)?

13 Signup and view all the answers

What is the primary characteristic of radicals such as NO?

They contain an unpaired electron. Signup and view all the answers

Which step is prioritized when completing octets in Lewis structures?

Complete the octet of the most electronegative atoms first Signup and view all the answers

Which step is NOT part of creating a Lewis dot structure?

Connect with double bonds. Signup and view all the answers

What does the term 'resonance' refer to in molecular structures?

The use of multiple Lewis structures for a single molecule Signup and view all the answers

In the NF3 molecule, how many total valence electrons are present?

21 Signup and view all the answers

Which Nobel Prize was awarded for research related to nitric oxide?

Physiology or Medicine Signup and view all the answers

What is determined first when drawing a Lewis structure?

The arrangement of atoms based on electronegativity Signup and view all the answers

What condition must be met for a central atom in a Lewis structure to not need any adjustments?

It satisfies the octet rule Signup and view all the answers

What is the primary function of superoxide dismutase in biological systems?

To catalyze the conversion of superoxide ion into oxygen and peroxide Signup and view all the answers

Which of the following reactive oxygen species is considered the most reactive?

Hydroxyl radical Signup and view all the answers

Which cellular component is NOT mentioned as a target for oxidation by reactive oxygen species?

Glucose Signup and view all the answers

What harmful effect can excess nitric oxide (NO) lead to in biological systems?

Formation of peroxynitrite Signup and view all the answers

What type of reaction does the superoxide dismutation process represent?

A disproportionation (dismutation) reaction Signup and view all the answers

What type of compounds are peroxynitrite considered as?

Oxidants and nitrating agents Signup and view all the answers

Which of the following options is a consequence of oxidative stress caused by reactive oxygen species?

Damage to DNA and proteins Signup and view all the answers

Which of the following statements about superoxide ion and reactive oxygen species is true?

Superoxide ion can cause oxidative damage in various cellular components. Signup and view all the answers

What is the bond order of each O-O bond in ozone (O3)?

1.5 Signup and view all the answers

Which of the following statements about resonance structures is true?

The actual structure of O3 is a hybrid of its resonance structures. Signup and view all the answers

What is the bond length of the O-O bonds in ozone compared to O=O and H-O-O-H?

Longer than O=O but shorter than H-O-O-H. Signup and view all the answers

How are the bond order and bond strength related?

Higher bond order indicates stronger bonds. Signup and view all the answers

What is the significance of a double-headed arrow in resonance structures?

It indicates that multiple structures can represent the molecule. Signup and view all the answers

When constructing a Lewis dot structure for CO32-, what is the first step?

Count the number of valence electrons on each atom. Signup and view all the answers

What does the bond length of 128 pm in ozone imply about its bonds?

The bonds are a hybrid of single and double bonds. Signup and view all the answers

Which of the following is NOT part of the process for drawing a Lewis structure?

Add lone pairs to all atoms evenly. Signup and view all the answers

Study Notes

Fundamentals of Medicinal and Pharmaceutical Chemistry

This presentation covers covalent bonding in physiologically important ions and molecules.
Essential concepts are covered in Chang and Goldsby's "Essential Concepts" textbook (Section 9.1, 9.2, 9.4 - 9.9).

Learning Outcomes

Construct Lewis dot structures for diatomic and triatomic molecules.
Define resonance.
Define bond order and its relation to bond strength/length.
Define free radical.
Identify nitric oxide, superoxide ion, and hydroxyl radical as free radicals.
Define disproportionation (dismutation) reaction.
Outline the equation for superoxide disproportionation and the role of superoxide dismutase.
Outline the equation for the reaction of nitric oxide and superoxide to form peroxynitrite.
Outline the neurotoxicity of peroxynitrite.

Lewis Dot Structures

A Lewis dot symbol shows the element symbol and one dot for each valence electron.
Valence electrons occupy the outermost shell and participate in bonding.
Lewis dot structures represent bonding in molecules and ions.

Six-Step Procedure for Lewis Dot Structures

Count the valence electrons for each atom (considering ionic charge).
Arrange the atoms in the molecule; hydrogen is generally excluded from the central atom.
Connect each central atom to the other atoms using a single bond.
Complete the octet rule for most electronegative atoms first by adding lone pairs. Hydrogen follows the duet rule.
If the central atom doesn't have a full octet, use electrons from surrounding atoms to form multiple bonds (double or triple).
Show any possible resonance forms.

Electronegativity Trends

Electronegativity increases across a period and decreases down a group in the periodic table.
The table provides Pauling scale values for relative electronegativity.

Resonance and Resonance Structures

Resonance involves using multiple Lewis structures to represent a molecule.
A molecule's actual structure is a hybrid of its resonance structures.
A double-headed arrow indicates resonance structures.

O-O Bond Properties in O₃

The two oxygen-to-oxygen bonds in ozone are experimentally identical in length.
The O-O bond lengths are 128 pm each, intermediate between a single and double bond.

Resonance Structures of O₃

Ozone's structure is a hybrid of resonance structures, so the bond order of each O-O bond is 1.5.

Bond Order

Bond order indicates the approximate bond strength.
A higher bond order correlates with a stronger bond.
Bond order is the number of connections between atoms.

Lewis Dot Structure for CO₃²⁻

Calculate the total valence electrons.
Arrangement of atoms and single bonds.
Complete the octet rule in most electronegative atoms (O) first, then on the central atom (C).
Determine any resonance structures.

Bond Order of C-O Bonds in CO₃²⁻

The C-O bonds in CO₃²⁻ are identical.
The actual structure is a hybrid of resonance structures, so the C-O bond order is 4/3.

Lewis Dot Structure for CO

Count the valence electrons for carbon and oxygen.
Arrange the atoms and form a single bond.
Complete octet rule for the oxygen atoms, then the carbon atom.
Check for any resonance structures.

Isoelectronic Structures

Isoelectronic structures have the same number of valence electrons and the same connectivity.
They share the same number of atoms and bonds.
Examples include N₂, CO, and NO⁺.

Limitations of Lewis Dot Structures

Lewis structures cannot always explain the paramagnetism observed in molecules like O₂.
Molecular orbital theory provides a more accurate explanation.

NO (Nitric Oxide)

NO is a molecule of the year 1992, a neurotransmitter, and involved in lowering blood pressure and antimicrobial defense.
NO relaxes muscle cells in the cardiovascular system.

Reactive Oxygen Species (ROS)

ROS are by-products of mitochondrial oxidation, including superoxide ion (O₂⁻), peroxide ion (O₂²⁻), and hydroxyl radical (OH).
Hydroxyl radical (OH) is the most reactive ROS.

Superoxide Ion (O₂⁻) and Superoxide Dismutase

Superoxide ion is a damaging reactive oxygen species that is removed by disproportionation (dismutation).
This enzyme-catalyzed reaction involves the simultaneous oxidation and reduction of oxygen.

Exceptions to the Octet Rule

Group 2A and 3A elements can form stable compounds with fewer than 8 electrons around the central atom (e.g., BeH₂).

Learning Outcomes (Recap)

Draw Lewis dot structures for diatomic and triatomic molecules using simple rules.
Define resonance, bond order, free radical, and disproportionation (dismutation).
Identify key molecules as free radicals.
Describe reactions related to peroxynitrite, superoxide dismutase and reactive oxygen species.

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Description

Explore the key concepts of covalent bonding in medicinal and pharmaceutical chemistry through this quiz. Based on Chang and Goldsby's 'Essential Concepts', this quiz covers Lewis structures, resonance, and the identification of free radicals. Test your understanding of bond order and the significance of superoxide dismutase and peroxynitrite in physiological processes.