Organic Chemistry I For Dummies book cover

Organic Chemistry I For Dummies

Author:
Arthur Winter
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Overview

Organic Chemistry I For Dummies, 2nd Edition (9781119293378) was previously published as Organic Chemistry I For Dummies, 2nd Edition (9781118828076). While this version features a new Dummies cover and design, the content is the same as the prior release and should not be considered a new or updated product.


The easy way to take the confusion out of organic chemistry

Organic chemistry has a long-standing reputation as a difficult course. Organic Chemistry I For Dummies takes a simple approach to the topic, allowing you to grasp concepts at your own pace.

This fun, easy-to-understand guide explains the basic principles of organic chemistry in simple terms, providing insight into the language of organic chemists, the major classes of compounds, and top trouble spots. You'll also get the nuts and bolts of tackling organic chemistry problems, from knowing where to start to spotting sneaky tricks that professors like to incorporate.

  • Refreshed example equations
  • New explanations and practical examples that reflect today's teaching methods
  • Fully worked-out organic chemistry problems

Baffled by benzines? Confused by carboxylic acids? Here's the help you need—in plain English!

Organic Chemistry I For Dummies, 2nd Edition (9781119293378) was previously published as Organic Chemistry I For Dummies, 2nd Edition (9781118828076). While this version features a new Dummies cover and design, the content is the same as the prior release and should not be considered a new or updated product.


The easy way to take the confusion out of organic chemistry

Organic chemistry has a long-standing reputation as a difficult course. Organic Chemistry I For Dummies takes a simple approach to the topic, allowing you to grasp concepts at your own pace.

This fun, easy-to-understand

guide explains the basic principles of organic chemistry in simple terms, providing insight into the language of organic chemists, the major classes of compounds, and top trouble spots. You'll also get the nuts and bolts of tackling organic chemistry problems, from knowing where to start to spotting sneaky tricks that professors like to incorporate.

  • Refreshed example equations
  • New explanations and practical examples that reflect today's teaching methods
  • Fully worked-out organic chemistry problems

Baffled by benzines? Confused by carboxylic acids? Here's the help you need—in plain English!

Organic Chemistry I For Dummies Cheat Sheet

You won't get very far in your study of organic chemistry without the periodic table of elements and an understanding of the common functional groups (or reactive centers) that dictate how most of a compound's chemical reactions occur.

About The Author

Arthur Winter, PhD, is the author of the popular Organic Chemistry Help! website chemhelper.com and Organic Chemistry I For Dummies. His professional focus is on the chemistry of magneto-organic materials.

Articles From The Book

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Chemistry Articles

Identifying Chiral Molecules, Meso Compounds, and Diastereomers

Chiral molecules usually contain at least one carbon atom with four nonidentical substituents. Such a carbon atom is called a chiral center (or sometimes a stereogenic center), using organic-speak. Any molecule that contains a chiral center will be chiral, with the exception of a meso compound (see below for how to identify these). For example, the compound shown here contains a carbon atom with four nonidentical substituents; this carbon atom is a chiral center, and the molecule itself is chiral, because it's nonsuperimposable on its mirror image.

A chiral center
You need to be able to quickly spot chiral centers in molecules. All straight-chain alkyl group carbons (CH3 or CH2 units) will not be chiral centers because these groups have two or more identical groups (the hydrogens) attached to the carbons. Neither will carbons on double or triple bonds be chiral centers because they can't have bonds to four different groups. When looking at a molecule, look for carbons that are substituted with four different groups. See, for example, if you can spot the two chiral centers in the molecule shown here.
A molecule with two chiral centers
Because CH3 and CH2 groups cannot be chiral centers, this molecule has only three carbons that could be chiral centers. The two leftmost possibilities, identified in the next figure, have four nonidentical groups and are chiral centers, but the one on the far right has two identical methyl (CH3) groups and so is not a chiral center.
The chiral centers in a long molecule

How to identify molecules as meso compounds

A meso compound contains a plane of symmetry and so is achiral, regardless of whether the molecule has a chiral center. A plane of symmetry is a plane that cuts a molecule in half, yielding two halves that are mirror reflections of each other.

By definition, a molecule that's not superimposable on its mirror image is a chiral molecule. Compounds that contain chiral centers are generally chiral, whereas molecules that have planes of symmetry are achiral and have structures that are identical to their mirror images.

The plane of symmetry in meso compounds
For example, cis-1,2-dibromocyclopentane (shown in the first figure) is meso because a plane cuts the molecule into two halves that are reflections of each other. Trans-1,2-dibromocyclopentane, however, is chiral because no plane splits the molecule into two mirror-image halves. Now look at the mirror images of these two molecules in the second figure to prove this generality to yourself.
The mirror images of achiral (meso) and chiral molecules
Even though the cis compound has two chiral centers (indicated with asterisks), the molecule is achiral because the mirror image is identical to the original molecule (and is, therefore, superimposable on the original molecule). Molecules with planes of symmetry will always have superimposable mirror images and will be achiral. On the other hand, the trans stereoisomer has no plane of symmetry and is chiral. In organic chemistry, you need to be able to spot planes of symmetry in molecules so you can determine whether a molecule with chiral centers will be chiral or meso. For example, can you spot the planes of symmetry in each of the meso compounds shown in the last figure?
Some meso compounds

How to Identify the Diastereomers of a Molecule

When more than one chiral center is present in a molecule, you have the possibility of having stereoisomers that are not mirror images of each other. Such stereoisomers that are not mirror images are called diastereomers.

Typically, you can only have diastereomers when the molecule has two or more chiral centers.

The maximum number of possible stereoisomers that a molecule can have is a function of 2n, where n is the number of chiral centers in the molecule. Therefore, a molecule with five chiral centers can have up to 25 or 32 possible stereoisomers! As the number of chiral centers increases, the number of possible stereoisomers for that compound increases rapidly. For example, the molecule shown here has two chiral centers.
A molecule with two chiral centers
Because this molecule has two chiral centers, it can have a total of 22, or 4, possible stereoisomers, of which only one will be the enantiomer of the original molecule.

Enantiomers are stereoisomers that are mirror images of each other.

Because both chiral centers in this molecule are of R configuration, the enantiomer of this molecule would have the S configuration for both chiral centers. All the stereoisomers of this molecule are shown in the next figure. Those molecules that are not enantiomers of each other are diastereomers of each other.
The four stereoisomers of a molecule with two chiral centers

Chemistry Articles

How to Find and Number the Longest Chain in a Branched Alkane

Alkanes are not limited to staying in a line — they can have structures that branch. When naming a branched alkane, your first step is to find and number the longest chain.

After you number the parent chain, if you want to name the branched alkane, you need to determine the names of all the substituents that stick off of the parent chain, and then order the substituents alphabetically in front of the parent chain.

This figure shows an example of a branching alkane. As you can see, the alkane with the formula C4H10 can have two possible chemical structures, or isomers — one alkane that’s a straight chain (butane), and one alkane that’s branched (isobutane).
The isomers of C4H10

Find the longest chain in a branched alkane

The first, and potentially the trickiest, step in naming a branched alkane is to find the longest chain of carbon atoms in the molecule. This task can be tricky because, as a reader of English, you’re so used to reading from left to right. Often, however, the longest chain of carbons is not the chain that follows simply from left to right, but one that snakes around the molecule in different directions. Organic professors like to make the parent chain one that curves around the molecule and doesn’t necessarily flow from left to right, so you have to keep on your toes to make sure that you’ve spotted the longest carbon chain.
The wrong and right ways to count the parent chain
The longest carbon chain for the molecule shown here is seven carbons long, so the parent name for this alkane is heptane.

Number the longest chain in a branched alkane

Number the parent chain starting with the end that reaches a substituent first. A chain can always be numbered in two ways. For the molecule in this example, the numbering could start at the top and go down, or it could start at the bottom and go up. The correct way to number the parent chain is to start with the end that reaches the first substituent sooner. A substituent is organic-speak for a fragment that comes off of the parent chain.
The right and wrong ways to number the carbons of the parent chain
As you can see here, if you number from the top down, the first substituent comes at carbon number three; if you number from the bottom up, the first substituent comes at carbon number four. The correct numbering in this case, then, starts at the top and goes down.

Chemistry Articles

How to Determine the R / S Configuration of a Chiral Center from a Fischer Projection

An easy way to find the R / S configuration of a molecule with more than one chiral center is with a Fischer projection. A Fischer projection is a convenient two-dimensional drawing that represents a three-dimensional molecule. To make a Fischer projection, you view a chiral center so that two substituents are coming out of the plane at you, and two substituents are going back into the plane, as shown here. Then the chiral center becomes a cross on the Fischer projection. Every cross on a Fischer projection is a chiral center.

Creating a Fischer projection
Fischer projections are convenient for comparing the stereochemistries of molecules that have many chiral centers. But these projections have their own sets of rules and conventions for how you can rotate and move them. As shown in the figure below, the two main ways to rotate a Fischer projection are as follows:

  • You can rotate a Fischer projection 180 degrees and retain the stereochemical configuration, but you cannot rotate a Fischer projection 90 degrees.

  • You can rotate any three substituents on a Fischer projection while holding one substituent fixed and retain the stereochemical configuration.

Working with Fischer projections
Here’s how to determine the configuration of a chiral center drawn in a Fischer projection: First, you prioritize each of the substituents using the Cahn–Ingold–Prelog prioritizing scheme.

According to the Cahn–Ingold–Prelog prioritizing scheme, the highest priority goes to the substituent whose first atom has the highest atomic number. (For example, Br would be a higher priority than Cl, because Br has a larger atomic number.)

Then, you put the fourth priority substituent on the top, and draw a curve from the first- to the second- to the third-priority substituent. If the curve goes clockwise, the configuration is R; if the curve goes counterclockwise, the configuration is S. To get the number-four priority substituent at the top of the Fischer projection, you have to use one of the two allowed moves diagramed in the second figure. (You can make a 180-degree rotation, or you can hold one substituent fixed and rotate the other three.) Two examples of the determination of the configuration from Fischer projections are shown here.
Determining R and S configurations from Fischer projections

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