Introduction to Organic Chemistry: Structure of Organic Molecules (Chem 14C)

Course Overview: Structure of Organic Molecules

Introduction

This course, Chem 14C, focuses on the structure of organic molecules, a foundational topic in organic chemistry. Organic chemistry is the study of carbon-containing compounds, which are central to biological systems and synthetic materials. The course is divided into two main parts: molecular structure and spectroscopy.

• Instructor: Dr. Martin-Louis Riu

• Lecture Times: MWF 2:00–2:50pm (CS 76), MWF 4:00–4:50pm (CS 50)

• Office Hours: Tues & Wed 5:00–5:50pm (Young Hall 4222-D1/2)

• Teaching Assistants: Multiple TAs with varied office hours (see syllabus for details)

What is Organic Chemistry?

Definition and Scope

Organic chemistry is the study of the compounds of carbon. It encompasses a vast array of molecules, including those found in living organisms (e.g., glucose, adenine) and synthetic materials (e.g., polyester).

• Chemistry: Study of matter and its transformations.

• Organic Chemistry: Focuses on carbon compounds, which can be natural or synthetic.

• Examples: Glucose (C6H12O6), Adenine (C5H5N5), Polyester (synthetic polymer).

Organic chemistry is typically broken down into:

• Structure: How atoms are arranged and bonded in molecules.

• Spectroscopy: Methods for analyzing molecular structure and composition.

Why Carbon is Unique

Properties of Carbon

Carbon's position on the periodic table gives it several unique properties that make it central to organic chemistry:

• Small atomic size

• Intermediate electronegativity

• Four valence electrons

These properties allow carbon to:

• Form strong bonds with a wide range of elements (including H, O, N, and P).

• Form strong bonds with itself, enabling long chains, rings, and complex molecular scaffolds.

• Form up to four covalent bonds, allowing for versatile bonding patterns.

Catenation is the ability of carbon to form chains and rings by bonding to itself, leading to a diversity of molecular structures (branched chains, linear chains, rings).

Course Structure and Logistics

Syllabus Highlights

• Required/Recommended Materials:

  • "Organic Chemistry: Structure and Function" (Volhardt and Schore; 8th edition) – optional

  • Molecular model kit – highly recommended

  • "Organic Chemistry as a Second Language" (David Klein) – highly recommended

• Lecture Format: Synchronous and in-person, with slides posted before class and lectures recorded for courtesy viewing.

• Discussion Sections: Attendance expected; provides up to 7% of total grade.

• Problem Sets: 7 sets (1 dropped), worth 21% of total grade; graded on completion.

• Exams: Two midterms (36%) and one final (36%), all in-person and closed-note.

• Extra Credit: iClicker questions (2%), teaching evaluations (0.4%), LA evaluations (0.2%).

Grading Breakdown

Assessment	Percentage
Discussion Section Attendance	7%
Problem Sets (x7)	21%
Midterm Exams (x2)	36%
Final Exam	36%
Total	100%
iClicker Questions (extra credit)	2%
Teaching Evaluation (extra credit)	0.4%
LA Teaching Evaluation (extra credit)	0.2%

Key Concepts in Organic Chemistry

Molecular Structure

Molecular structure refers to the arrangement of atoms and the distribution of electrons in a molecule. Understanding structure is essential for predicting chemical behavior and reactivity.

• Electron distribution: Determines molecular polarity and interactions.

• Spatial arrangement: Influences physical and chemical properties.

• Example: Water (H2O) has a bent structure with a bond angle of 104.5°, leading to its polar nature.

Coulomb Forces and Bonding

Coulomb's Law describes the attraction and repulsion between charged particles:

• Opposite charges attract (e.g., electrons and protons).

• Like charges repel (e.g., electrons).

Coulomb's Law:

$F = k \frac{q_1 q_2}{r^2}$

where $F$ is the force, $q_1$ and $q_2$ are charges, $r$ is the distance between charges, and $k$ is a constant.

Ionic and Covalent Bonds

Bonds are classified based on how electrons are distributed between atoms:

• Covalent bond: Formed by sharing electrons between atoms.

• Ionic bond: Based on electrostatic attraction between ions of opposite charge.

Most bonds exist on a spectrum between purely covalent and purely ionic, with electron density often polarized.

Electronegativity and Bond Type

Electronegativity is a measure of an atom's ability to attract electrons in a chemical bond. It increases left to right across a period and bottom to top in a group.

Difference in Electronegativity	Type of Bond
Less than 0.5	Nonpolar covalent
0.5 to 1.9	Polar covalent
Greater than 1.9	Ionic

Example: H–Cl bond has a difference in electronegativity of 0.9, making it a polar covalent bond.

Molecular Dipoles

A molecular dipole results from the vector sum of all individual bond dipoles in a molecule. For example, although the C=O bonds in CO2 are polar, the molecule is linear and symmetric, resulting in no net dipole moment (CO2 is nonpolar).

Consequences of Polar Bonds and Dipoles

Polar bonds and molecular dipoles lead to various intermolecular interactions:

• Dispersion forces: Temporary, nonpolar interactions; generally weak.

• Dipole-dipole interactions: Permanent, polar interactions; stronger than dispersion forces.

• Hydrogen bonding: A special case of dipole-dipole interaction, particularly strong when H is bonded to N, O, or F.

Course Success Tips

Study Strategies

• Practice problems regularly; do not rely solely on reading or watching lectures.

• Utilize available resources: discussion sections, office hours, study groups, flashcards, and quizzes.

• Stay current with homework and review material before lectures.

• Struggle through problems before consulting solutions to enhance learning and retention.

Additional info: The syllabus emphasizes active learning and metacognition, encouraging students to engage deeply with the material for success in organic chemistry.