Organic Chemistry I For Dummies
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!
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About The Author
Arthur Winter is a graduate of Frostburg State University, where he received his BS in chemistry. He received his PhD at the University of Maryland in 2007. He is currently a chemistry professor at Iowa State University.
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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.Common functional groups in organic chemistryIn organic chemistry, functional groups (or reactive centers) are small structural units within molecules that dictate how most of the compound’s chemical reactions occur.
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Organic chemistry has a reputation for being a challenging course. But here’s the thing that’s often not mentioned: Organic chemistry is a subject that anyone can ace. Doing well, though, requires working not only hard but also efficiently. Here are ten practical tips on how to study as efficiently as possible so you can do well in the class.
Chemistry
Suppose you’re working an organic chemistry assignment, and you're asked to propose a mechanism for the conversion of the alcohol shown in the following figure to the alkene shown in the same figure.
An example mechanism problem.
First, you want to identify what kind of mechanism you’re dealing with. Is it an acid or a base mechanism?
Chemistry
In this article, we look at how electron-donating and electron withdrawing substituents direct the substitution on a benzene ring.
Electron-donating substituents
In the synthesis of disubstituted benzenes, the cation resulting from ortho-para addition with electron donors will be more stable than the meta-derived cation.
Chemistry
An extremely useful reaction for making alcohols is the Grignard reaction (pronounced grin-yard). To make alcohols using the Grignard reaction, you react a "Grignard reagent" with a carbonyl compound. Making a Grignard reagent is fairly simple: You simply add magnesium to an alkyl halide, as shown here, which inserts the magnesium into the C-X bond to make the Grignard reagent.
Alkyne reactions are similar to those of the alkenes, and these reactions use reagents similar to those used in alkene reactions. Alkynes can form a variety of functional groups, including tetrabromides, alkanes, alkenes, ketones, and aldehydes.
Brominate an alkyne to form a tetrabromide
Bromine reacts with the pi bond in alkynes to make the dibromide via the same mechanism as bromine addition to alkenes (think "bromonium ion").
Chemistry
For many students of organic chemistry, it’s easy to become bogged down in the minutiae of organic molecules and their reactions and forget that organic compounds actually form the backbone of all living things.
For example, when learning about alkenes (carbon-carbon double bonds) and their properties, you learn that two stereoisomers are often possible — the cis isomer, where two substituents are oriented off the same side of the double bond, and the trans isomer, where the two substituents are oriented off the opposite side of the double bond.
Elimination reactions often compete with substitution reactions. As in substitution reactions, one possible mechanism for an elimination reaction is first-order elimination, or the E1 mechanism. The general form of an elimination reaction is shown in the first figure. In this reaction, a substrate (typically, an alkyl halide) eliminates one equivalent (unit) of acid to make an alkene.
Elimination reactions often compete with substitution reactions. As in substitution reactions, one possible mechanism for an elimination reaction is second-order elimination, or the E2 mechanism. The general form of an elimination reaction is shown in the first figure. In this reaction, a substrate (typically, an alkyl halide) eliminates one equivalent (unit) of acid to make an alkene.
Chemistry
When you synthesize disubstituted benzenes, and the first added group is an electron-withdrawing substituent, this group usually directs incoming electrophiles to the meta position (shown in the first figure).
The ortho, meta, and para positions
For example, take the bromination reaction of nitrobenzene, shown in the next figure.
Chemistry
Ozonolysis is a way of cleaving carbon-carbon double bonds into two fragments using ozone (O3) as a reagent. The fragments formed are either aldehydes or ketones, depending on the nature of the R groups attached to the double bond, as shown here.
The ozonolysis of an alkene.
If both R groups on one side of the double bond are alkyl groups, that side of the double bond will become a ketone fragment; if only one R group is an alkyl group and the other R is a hydrogen, that side of the double bond will become an aldehyde fragment.
Chemistry
A first-order (or SN1) substitution reaction occurs when one group on an organic molecule leaves and is later substituted by another group. This reaction goes through a carbocation intermediate. The SN1 mechanism is analogous to breaking up with your current significant other, staying single for a while, and only after you've been single, becoming attached to a new romantic partner.
Mass spectrometry provides valuable information about the structure of a molecular compound, including its isotopes. Because mass spectrometry determines the weights of fragments, atoms that naturally have heavy isotopes become important.
Isotopes are atoms that have the same number of protons and electrons, but different numbers of neutrons.
Chemistry
A mass spectrometer can help you locate unknown ions in the mass spectrum so that you can identify them. When charged particles move through the magnetic field of a mass spectrometer, they're deflected (pulled off course) by the magnetic field; they then hit the detector, as the first figure shows.
The inside of a mass spectrometer.
Chemistry
Mass spectrometry (also called mass spec) provides valuable information about the structure of molecular compounds. Organic chemists can use a mass spectrometer to ionize — or "smash" — a molecular compound in gaseous form, sort the fragments, and then identify the molecule fragments based on their molecular weights.
Chemistry
A substitution reaction follows a fairly simple form: one group simply substitutes for another in the reaction, as shown here. Whether or not it follows the second-order mechanism depends on certain factors.
A substitution reaction.
Two mechanisms are actually possible for substitution, the SN1 mechanism, and the SN2 mechanism (shown in the next figure).
Chemistry
After molecules are ionized in a mass spectrometer, they become radical cations that can then be sorted and weighed. Some of these radical cations can also rearrange after being ionized. The most famous rearrangement is called the McLafferty rearrangement.
A radical cation is a cation with an unpaired electron.
Chemistry
Any chiral center can have two possible configurations, and these configurations are designated either R or S by convention (the letters R and S come from the Latin words for right and left, rectus and sinister). If a molecule has a chiral center that is designated R, the chiral center will be S in the molecule's enantiomer.
Classifying and naming alcohols is fairly straightforward. For example, to classify an alcohol, you just need to know where the hydroxyl group is in the alcohol molecule. Naming an alcohol does require a few steps, but if you know how to name alkanes, then you'll have no problems.Alcohols are molecules that contain a hydroxyl (OH) group, and they're typically classified by the carbon to which the hydroxyl group is attached.
Chemistry
Hydration, or adding water across a double bond to make an alcohol, is a reaction that's similar to the addition of a hydrohalic acid across a double bond. Two different reactions accomplish the hydration. The first reaction adds the alcohol (OH group) to the most substituted carbon on the double bond to make the Markovnikov product, and the complementary reaction puts the alcohol on the least substituted carbon in the double bond to make the anti-Markovnikov product.
Chemistry
When you want to identify the structure of a molecular compound, your first step is to determine the degrees of unsaturation from its molecular formula. This gives a quick indication of whether the compound contains rings, double bonds, or triple bonds, or whether the molecule is saturated.
This is only the first step in finding the molecular structure.
Chemistry
Hydrogen NMR (often called proton NMR or 1H NMR) is often the most useful NMR (nuclear magnetic resonance) type for organic chemists.For example, the 1H NMR shows you the NMR peaks that represent particular functional groups in a molecular formula (specifically, carboxylic acids, aldehydes, and aromatic rings).
Chemistry
When you use hydrogen NMR (or 1H NMR) to determine how many hydrogens are in a molecule, this only gives you the relative number of hydrogens, not the absolute number. For example, say that your relative ratio of hydrogens is 1:2, as shown here.
By measuring integration curves from NMR peaks, you find a relative ratio of 1:2.
Chemistry
You can determine whether a ring system is aromatic, anti-aromatic, or non-aromatic by determining whether it meets certain conditions. To be aromatic, a molecule must meet four conditions:
It must be a ring.
It must be flat (planar).
It must have in each atom of the ring a p orbital that's orthogonal to the plane of the ring.
Chemistry
Knowing the number of degrees of unsaturation in a molecule is useful because this number is related to how many multiple bonds or rings are present in an unknown compound. (This morsel of information becomes very useful when you want to determine the structure of an unknown compound.)
One double bond, one degree of unsaturation
The degrees of unsaturation in a molecule are additive — a molecule with one double bond has one degree of unsaturation, a molecule with two double bonds has two degrees of unsaturation, and so forth.
Chemistry
In addition to being one of the most valuable reactions in organic chemistry, Diels–Alder reactions also tend to look very confusing. Fortunately, you can follow these four simple steps to determine the products of these reactions:
Orient the diene and the dienophile correctly.
In this step, you make sure that the double bonds are oriented correctly (the diene double bonds are pointing in the direction of the dienophile), and that the diene is in the s-cis conformation (if it isn't, you need to rotate it so that it is).
Chemistry
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.
Chemistry
When you have identified all the fragments of a molecular compound, you can use information such as NMR peak splitting, chemical shift, and degrees of unsaturation to help identify the compound's final structure.
Often, when you're starting, the best way to go from fragments to a possible structure is to simply brainstorm all the possible molecules that could include the fragments you listed, because in many cases there will be more than one way to put all the fragments together.
Chemistry
If you are given a mass spectrum for a molecule, you may be asked to draw the structures for certain molecular fragments based on where they appear in the mass spectrum.
A sample problem
For example, here is a sample question of the type you may see on an exam: The mass spectrum for 2-pentanone is shown here. Draw the fragments responsible for the peaks in the mass spectrum at m/z 71, 58, and 43.
Chemistry
Although the hydrocarbon cyclohexane is typically drawn as if it were flat, in reality the structure is not flat at all. Most of the time, the structure exists in what is called the chair conformation. This conformation is called the chair because it looks (sort of) like a reclining lounge chair, as shown here.
Chemistry
IR (infrared) spectroscopy is useful in organic chemistry because it enables you to identify different functional groups. This is because each functional group contains certain bonds, and these bonds always show up in the same places in the IR spectrum.
Functional groups are the portions in an organic molecule that dictate how the molecule will react.
Chemistry
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.
Chemistry
The first step in drawing the most stable conformation of cyclohexane is to determine — based on whether the substituents are cis or trans to one another, and based on where they're located on the ring — what the choices of axial and equatorial positions are for the substituents. A handy way of determining the substitution alternatives is to use the Haworth projection, as shown here.
Chemistry
Alcohols and amines are fairly easy to identify in the IR spectrum, based on their relative locations and shapes. The first thing you'll notice is that both of these functional groups appear to the left of the C-H absorptions, which always occur between 2,800 cm–1 to 3,000 cm–1 in the IR spectrum.
Absorption of alcohol.
Chemistry
You can locate carbonyl groups, alkenes, alkynes, and aromatics in the IR (infrared) spectrum, based on their shapes and relative locations. For one thing, all of these functional groups appear to the right of the C-H absorptions, which always occur between 2,800 cm–1 to 3,000 cm–1 in the IR spectrum, and to the left of the fingerprint region (below 1,500 cm–1).
Chemistry
Whether through alpha cleavage or loss of a water molecule, molecular fragmentation in a mass spectrometer tends to follow certain patterns. You can often predict what peaks will be observed in the mass spectrum simply by looking at a molecule's structure and seeing which pieces would be easy to break off to make stable cations.
Chemistry
When trying to determine the structure of a compound based on its molecular formula, you can use nuclear magnetic resonance (NMR) and infrared (IR) spectroscopy to help you identify the fragments of the molecule. (Once you identify these fragments, you can identify the molecule’s structure.)After you’ve determined the number of hydrogen atoms that each NMR peak represents, you can assign each peak to a fragment of the molecule.
Any molecule that contains a chiral center will be chiral, with one exception: a meso compound. 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.
Chemistry
When searching for the substituents in a branched alkane, you may run across some situations where you aren't sure how to proceed. For example, what do you do when there are two or more instances of the same substituent? And what if a complex substituent appears on one of the branches?
When naming a branched alkane, you first need to locate and number the parent (longest) chain.
Alkenes, which are molecules containing carbon-carbon double bonds, have the possibility of having stereoisomers, just as ring systems do. This is because, unlike carbon-carbon single bonds, which are free to rotate, double bonds are fixed and rigid. In other words, rotation around carbon-carbon double bonds is not possible at reasonable temperatures.
Aromatics are a class of ring compounds that contain double bonds. The name aromatic comes from the fact that many of the simple aromatic compounds that were first isolated were highly fragrant; the lovely odors of such substances as vanilla, almond, and wintergreen are due to the presence of aromatic compounds in these products.
Alkynes are molecules that contain carbon-carbon triple bonds. They are named under the systematic nomenclature scheme in the same way that alkenes are, except that instead of the name ending with the suffix –ene, the names of alkynes end with the suffix –yne. As with alkenes, a number in the prefix is used to indicate the position of the alkyne in the molecule, as shown here.
Chemistry
When naming a branched alkane, after you locate and number the parent (longest) chain, you need to locate and identify all the substituents that stick off of the parent chain, and then order the substituents alphabetically in front of the parent chain.
Locate and identify the substituents in a branched alkane
For example, say you have a heptane molecule with two substituents coming off the parent chain — one substituent at carbon number three, and one substituent at carbon number four, as shown here.
Chemistry
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.
Chemistry
It's just as important to be able to determine and draw the structure of an organic molecule from its name as it is to be able to determine the name of its structure. Although English reads from left to right, the best way to read a structure's name is from right to left. For example, if you want to draw the structure for 4-t-butyl-2,3,5-trimethylheptane, you would start by first drawing the parent chain — heptane.
Chemistry
You can use integration curves on the nuclear magnetic resonance (NMR) spectrum to show peak intensities. The peak intensity — or the area underneath a peak on the NMR spectrum — is related to the number of hydrogens that the peak represents.Traditionally, integration is shown on the spectrum by the addition of an integration curve (as shown in the figure), although modern computing has made digital integration common that doesn't require you to do any measuring.
Chemistry
In general, the strength of an acid in an organic compound is directly proportional to the stability of the acid's conjugate base. In other words, an acid that has a more stable conjugate base will be more acidic than an acid that has a less stable conjugate base.
Acidic molecules generally have structural features that allow the anion in the conjugate base to delocalize the charge over a larger space.
Chemistry
If you know how to name alkanes, adding alkene nomenclature to your repertoire is a fairly straightforward task.Whereas the names of alkanes end with the suffix –ane, alkenes end with the suffix –ene. A two-carbon alkene, therefore, is named ethene; a three-carbon alkene is named propene, and an alkene in a five-membered ring is named cyclopentene, as shown here.
Chemistry
pKa values allow you to predict the equilibrium direction of acid-base chemical reactions for organic molecules. The pKa value of an acid is a quantitative measurement of a molecule’s acidity. The pKa is derived from the equilibrium constant for the acid’s dissociation reaction, Ka, and uses a logarithmic scale to allow the pKa values to span wide ranges.
Chemistry
Every hydrogen in a molecule that's in a unique chemical neighborhood will show up as a peak on a nuclear magnetic resonance (NMR) spectrum. Two (or more) hydrogens that have equivalent chemical neighborhoods, though, will be represented by just a single peak. Such hydrogens that are in identical chemical environments are said to be chemically equivalent.
Chemistry
When dealing with aromatic compounds, you often need to predict the acidities and the basicities of double bond–containing rings, including aromatic rings. For example, you may need to determine which one of two double bond–containing rings is more acidic, such as the molecules shown here.
Cyclopentadiene and cycloheptatriene—which is more acidic?
Chemistry
When four nonidentical groups are attached to a double bond in an alkene, you must use the E/Z system of nomenclature to assign the stereochemistry of the double bond. (E stands for the German word entgegen, which means "opposite," while Z stands for the German word zusammen, which means "together.")
To use the E/Z system of nomenclature, you have to play a game of high-low.
Chemistry
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).
Chemistry
One of the best ways to look at different conformations of straight-chain alkanes (individual conformations are called conformers) is to use Newman projections. A Newman projection is a convenient way of sighting down a particular carbon-carbon bond.
Straight-chain alkanes can exist in different conformations — different spatial arrangements of atoms that can be interconverted by rotation about a single bond — where not all the conformations are of equal energy.
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.Common functional groups in organic chemistryIn organic chemistry, functional groups (or reactive centers) are small structural units within molecules that dictate how most of the compound’s chemical reactions occur.
Here's something to remember as you study organic chemistry: Life is built on chiral building blocks — that is, the molecules that make up living things have a particular handedness (designated as R or S), and nature only uses one handedness and not the other.
In Alice in Wonderland, Alice is transported through the looking glass into a world that is the mirror image of our world.
Chemistry
When elements combine through chemical reactions, they form compounds. When compounds contain carbon, they’re called organic compounds. The four families of organic compounds with important biological functions areCarbohydratesThese molecules consist of carbon, hydrogen, and oxygen in a ratio of roughly 1:2:1.
Chemistry
Spectroscopy plays an increasingly important role in modern sports and culture. For instance, the sports of baseball and cycling (among others) have been roiled by cheating scandals in which athletes have tested positive for performance-enhancing drugs. But how do you actually test for whether an athlete has doped?
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