Organic Chemistry (CHM 221) Chapter 5.1

Study Notes

This chapter focuses on the orientation of molecules and how their 3-D structure affects reactions.
Specific products can have similar appearances but differ in the position of atoms or functional groups when their bonding orientations are compared.
The chapter primarily emphasizes concepts rather than chemical reactions.
The chapter is divided into two parts to allow homework assignments to be completed.

Stereochemistry investigates the 3-D structure of molecules.
Subtle differences in molecular shape can lead to significant variations in properties.
Examples include glucose and galactose, which have differing melting points and sweetness despite similar formulas.

Cellulose utilizes equatorial bonds to link rings, while starch uses one equatorial and one axial bond.
This difference in bonding leads to humans being able to metabolize starch for energy but not digest cellulose.

Isomers are different compounds with the same molecular formula.
Two main categories are constitutional isomers and stereoisomers.
Constitutional isomers have different IUPAC names and different physical and chemical properties despite identical molecular formulas.
Stereoisomers have identical IUPAC names (except for prefixes like cis or trans), identical functional groups, but different 3-D arrangements leading to potential differences in properties.

Examples provided include 2-methylpentane and 3-methylpentane as constitutional isomers.
Cis-1,2-dimethylcyclopentane and trans-1,2-dimethylcyclopentane are stereoisomers of the same molecular formula.

Examples like H₂O and CH₂BrCl are given as achiral molecules whose bonds and atoms align when superimposing mirror images.

A stereogenic center is a point in a molecule where the interchange of substituents creates a stereoisomer.
This is not always an atom, but could be any point in the molecule.
Identifying tetrahedral carbon atoms that have four different groups attached is key to finding stereogenic centers.
Groups like CH₂ and CH₃, and sp or sp² hybridized carbons are not considered stereogenic centers.

Rotation can provide a planar symmetry in some cases, making a molecule achiral.

One enantiomer can have beneficial effects while the other is detrimental or even toxic.
The example of naproxen and liver toxicity is used.

Enantiomers are drawn by first arbitrarily placing the groups around a stereogenic center and then reflecting the molecule to produce the mirror image.

The fundamental question about chirality is whether a molecule and its mirror image are superimposable.
If not, the molecule is chiral and no plane of symmetry is present.
Enantiomers are a pair of molecules that aren't superimposable but are mirror images.
Stereogenic centers are critical to determining chirality.

The homework problems focus on 5.2 (pg 182), 5.3, 5.6 (a, b, c), 5.9 (a, b), and problems related to molecules getting larger like 5.8.
Problem 5.2(further details on pg 188) should be studied in detail.
Other assigned end-of-chapter problems include 5.41 (a & b), 5.42 (a & b), and 5.43.