Review of First-Semester Organic Chemistry

andFunctional Groups

(20 Points)

During this lab period, we will review some of the important principals of organic chemistry. The functional groups that were introduced during the first semester will also be reviewed and some new ones introduced. Your grade on this lab will be your score on a 20-point diagnostic evaluation of your knowledge of bonding and organic families, as presented in the following pages. After you complete the two self-quizzes, see the instructor who will give you the 20-point evaluation. Complete the 20-point evaluation and turn it in to the instructor.

Organic Compounds Organic compounds contain carbon. The word compound means an electrically neutral

aggregate or collection of molecules or ions. As a simplification, there are three kinds of organic compounds, covalent compounds. salts and organometallic compounds. The most common type of organic compound contains only carbon and other nonmetals such as hydrogen, oxygen or nitrogen. Atoms of nonmetals are joined together by covalent bonds to form molecules. Thus, the compounds that contain only nonmetals are called covalent compounds. If a metal is part of the compound, the compound is an ionic compound, because metals form ions. When the metal is bonded to an atom other than carbon, the ionic compound is a salt. When the metal is bonded to carbon, the ionic compound is an organometallic compound.

Covalent Compounds Carbon is a nonmetal and forms covalent bonds with other nonmetals. A covalent bond is

two electrons or a pair of electrons that hold two atoms together. Thus, when carbon and another nonmetal form a bond, that bond is a covalent bond. When only carbon and hydrogen form a molecule, that molecule is a hydrocarbon. The simplest compound between carbon and hydrogen contains only one carbon. Carbon has a normal covalence of four and hydrogen one. Therefore, the simplest molecule is methane, CH4. The compound methane contains an aggregate or collection of methane molecules. Depending on the circumstances, the word methane can refer to one molecule of methane or to a collection of methane molecules. The context of its usage determines the meaning.

Ionic Compounds—Salts and Organometallics

1

When a compound contains a metal, it is either a salt or an organometallic compound. Organic acids are readily converted into salts by sodium hydroxide. The product is a salt, because the sodium is bonded to oxygen, a heteroatom. When butyl bromide reacts with lithium metal to form lithium bromide and butyl lithium, the butyl lithium is an organometallic compound because lithium is bonded to carbon.

Problem 1. Classify each of the following compounds as a covalent compound, a salt, or an organometallic compound.

acetone ethyl alcohol butane sodium acetate sodium acetylide

Solution 1. Step 1. Draw the structure of each compound, showing the bonding.

Step 2. Look at each structure. If the structure has no metal atoms, it is a covalent compound. If the structure has one or more metal atoms, it is either a salt or an organometallic compound. Thus, acetone, ethyl alcohol and butane are covalent compounds, and butane is a hydrocarbon.

Step 3. If the structure contains a metal, determine whether the metal is bonded to carbon or to a heteroatom. In sodium acetate, the metal sodium is bonded to oxygen. Therefore, sodium acetate is a salt. In sodium acetylide, the metal sodium is bonded to carbon. Therefore, sodium acetylide is an organometallic compound.

Bonding in Organic CompoundsOne property of carbon is that it forms single bonds, double bonds and triple bonds. Two

carbon atoms can join by single, double or triple bonds. In a complete molecule, each carbon atom will have four bonds. Let us consider two carbon atoms joined in turn by a single bond, a double bond and a triple bond. Carbon must have four bonds. Thus, hydrogen is necessary to make sure carbon always has four bonds in stable organic molecules. We classify organic

2

compounds into families. Hydrocarbons with only single bonds are alkanes, those with double bonds are alkenes, and those with triple bonds are alkynes.

The hydrocarbon families are very useful in the study of covalent bonding. A covalent bond is a pair of electrons that join two atoms. Another way of looking at a covalent bond is that the two electrons exist in a space between the two atoms. In most cases, one electron comes from each atom. In an ideal or hypothetical way, we can consider the individual atoms joining to make a molecule. Thus, we need two carbon and six hydrogen atoms to make ethane. When the atoms join, only the valence electrons will be involved in bonding. Valence electrons are found in the outermost shell of an atom. Each main shell of an atom has subshells that consist of orbitals. Any given orbital can have zero, one or two electrons in it. For hydrogen, there is only one main shell (1) and one orbital (s). Thus, we can describe the one electron of a given hydrogen atom as a 1s or simply s electron. Every hydrogen atom contains an s electron in an s orbital. The shape or geometry of an s orbital is a sphere. The one electron gets its name from its orbital. Remember that the orbital is the three-dimensional space where the electron is found. A general principal is that an orbital can hold a maximum of two electrons. The lone s electron of hydrogen is a valence electron, because it is found in the outermost main shell. A carbon atom contains six electrons and has the electron configuration 1s22s22p2. The outermost main shell of carbon is shell 2, which has four electrons. Thus, carbon has four valence electrons. The second main shell of carbon has two subshells s and p. Like the first main shell, this s subshell is simply one spherical s orbital that can hold two electrons as a max. The p subshell contains three p orbitals. These three orbitals are labeled px, py, and pz just so we can tell them apart. Each of these orbitals can hold a maximum of two electrons. From the electron configuration, we see that carbon has two p electrons. One of these electrons is found in the px orbital and the other in the py

orbital. Each p orbital gets one electron before any p orbital gets two electrons (Hund’s rule). The shape of p orbitals is like a dumbbell, with a node in the middle. The orbital representations of hydrogen and carbon atoms are shown on the next page. In our hypothetical model, we will have these atoms join to make molecules.

3

Figure 1. Atomic Orbitals of Hydrogen and Carbon

Atomic and Molecular HydrogenConsider the formation of molecular hydrogen from atomic hydrogen. Molecular

hydrogen has the formula H2 and forms from two hydrogen atoms. That is, we make a covalent bond between two hydrogen atoms. The covalent bond is two electrons, which hold the molecule together. The following equation shows the formation of H2 from two hydrogen atoms.

2 H• H2 = H-H

Let’s look at the actual formation of the covalent bond. The one electron of each hydrogen atom is found in an s orbital. The orbitals are where the electrons are found.The s orbitals are spherical spaces where the electrons are found. The two orbitals that contain valence electrons come together and share the same space. When two orbitals share the same space, they are said to overlap. The two electrons, one from each orbital of each H atom can now be found in the overlapped space. The two electrons in the same space make a covalent bond when they join two atoms together. That is, they are bonding electrons, because they make a bond. When two valence electrons share the same space but do not form a bond between two atoms, they are called nonbonding electrons.

Overlap of Two s Orbitals

4

Note that we start with two atoms of hydrogen and we form one hydrogen molecule. We also start with two atomic orbitals, and we form two molecular orbitals. Thus, when we overlap two atomic orbitals, we make two new molecular orbitals. The two atomic orbitals are in different atoms. The two molecular orbitals are within the same molecule.

All orbitals can hold a maximum of two electrons, whether they are atomic or molecular orbtials. Thus, the two electrons go into the lowest energy molecular orbital called a sigma () orbital. The higher energy orbital called sigma star (*) is empty, because we have only two electrons. In the valence-bond theory of bonding, we generally ignore the * orbital. The * orbital is an antibonding orbital. Antibonding orbitals are important in the molecular orbital (MO) theory of bonding. The bond between two hydrogen atoms is a single bond that forms by the overlap of one s orbital with another s orbital. The bond is called a sigma or bond. The bond is called a bond because it is formed by the overlap of two s orbitals. That is s + s = sigma is a Greek s). The two electrons share the space on a straight line between the two hydrogen nuclei. Since a hydrogen atom has only one s orbital, a hydrogen atom can only make bonds. This is true when H bonds with itself to form H2 and when it bonds with carbon or any other nonmetal atom. In a sense, hydrogen is simply necessary in many organic compounds to fill up the bonding sites of carbon. For example, hydrocarbons are made up of carbon backbones and filled in with hydrogen. Every time hydrogen forms a bond with carbon, that bond is called a sigma bond. Let us see how hydrogen bonds with carbon to make methane.

MethaneIn order to make methane, four hydrogen atoms must form bonds with one carbon atom. Since hydrogen is involved, we know that every bond will be called a sigma bond. Let us see how these four bonds are formed. To understand how the atomic orbitals overlap, we must go back to Figure 1 and see how the valence electrons are distributed in carbon. We know that the four hydrogen atoms each have one valence electron in an s orbital.

5

Figure 2. Valence Electrons in a Carbon Atom

The valence electrons in a carbon atom are distributed as shown in Figure 2. The s orbital has two electrons, and two p orbitals each have one electron. Four H atoms cannot bond to one C atom that has this orbital arrangement and give four identical bonds. Linus Pauling recognized this fact and concluded that the four valence orbitals of a carbon atom must change into four identical orbitals. We now call this process hybridization. To form methane, a carbon atom undergoes hybridization and forms a hybridized carbon atom called a sp3-hybridized carbon atom. The four valence electrons are then redistributed so that each of the four identical sp3 orbitals gets one electron. Figure 3 shows the sp3 hybridization of a carbon atom.

Figure 3. sp3 Hybridization of a Carbon Atom

When atomic carbon goes to an sp3 carbon, the name of the carbon atom and the name of the four identical orbitals are sp3. Thus, an sp3-hybridized carbon atom has four sp3-hybrid orbitals. The symbol sp3 means that four atomic orbitals—an s and three p orbitals have changed into four new sp3 orbitals. The symbol is pronounced ess pee three. From the pronunciation, we get one s and three p orbitals. The symbol tells us exactly how many and which orbitals were combined to make an sp3-hybridized carbon atom.Three general principals about hybrid orbitals are:1. Hybrid orbital all have the same shape—a teardrop shape. 2. Hybrid orbitals always repel each other and orient as far away as possible from other hybrid orbitals.3. Hybrid orbitals always form sigma () bonds.How will the four sp3 orbitals of an sp3-hybridized carbon orient?

6

Answer: The four hybrid orbitals repel each other and orient to be as far away from each other as possible. That gives a tetrahedral orientation of the four orbitals. Figure 4 shows how the four hybrid orbitals orient in an sp3-hybridized carbon atom to make methane.

Figure 4. Orientation of sp3-hybrid orbitals of a sp3-hybrid carbon atom.

When carbon is part of a molecule, it is always a hybridized carbon atom. Hybrid orbitals always make sigma bonds. Therefore, when we form the four bonds of methane, they will all be sigma bonds. Covalent bonds are made by the overlap of two orbitals, making a three dimensional space for two electrons. The sp3-hybridized carbon atom has four sp3–hybrid orbitals that must overlap with four s orbitals from four hydrogen atoms. Figure 5 shows how these orbitals overlap.

Figure 5. Orbital Overlap in Methane

Methane has four bonds. Each bond is made by the overlap of an sp3 orbital with an s orbital. Each bond is a sigma bond. An sp3 + s = sigma bond (Note: a sigma bond forms whenever two orbitals that start with the letter s overlap). Now, let’s start with methane, and

7

determine its bonding. Methane has the formula CH4. We know that hydrogen can form only sigma bonds. So the four bonds must all be sigma bonds. We also know that the carbon atom of methane has four identical sp3-hybrid orbitals and that all hybrid orbitals only make sigma bonds. So all four bonds must be sigma bonds. Sigma bonds from one atom always orient as far away from each other as possible. How do we know this? Because these bonds are made up of hybrid orbitals, and the hybrid orbitals, where the electrons are found, are as far away from each other as possible. Therefore, electrons, which are found in these orbitals, are also as far away from each other as possible. The structure of methane is shown below.

We can tell from the structure whether hybrid or unhybridized orbitals are involved. From the structure we see that the carbon atom has four sigma bonds. That means that all four of the carbon atom’s bonding orbitals are hybrid orbitals, because hybrid orbitals always make sigma bonds. To get four hybrid orbitals we need to blend or hybridize four atomic orbitals--one s and three p atomic orbitals, and we get four sp3-hybrid orbitals. The carbon atom must be sp3 hybridized, because it has four sp3 orbitals. The name of the hybridized carbon atom is the same as the name of its hybrid orbitals. An sp3-hybridized carbon atom has four sp3 orbitals.

EthaneEthane has the structure shown below.

All of the bonds are bonds. What kinds of orbitals overlap to make the bond between the two carbon atoms? Answer: An sp3 hybrid overlaps with an sp3 hybrid. An sp3 + sp3 makes a sigma bond. A general rule is that anytime an orbital with an s in its symbol overlaps with another orbital with an s in its symbol, we get a sigma bond. Ethane is made up of two carbon and six hydrogen atoms. Each hydrogen has one electron to donate to its bond with carbon, and each carbon has four electrons to donate, one to each bond. Hydrogen can only make sigma bonds, so the s orbital of each H atom overlaps with an sp3 orbital of a carbon atom to make a bond. Therefore, a sigma bond can arise from the overlap of a spherical s orbital with a teardrop hybrid orbital. A sigma bond can also arise from the overlap of two hybrid orbitals. Hybrid orbitals always make sigma bonds. Figure 6 shows the formation of sigma bonds.

8

Figure 6. Three Ways to Make a Sigma Bond

EtheneEthene has the structure shown below.

Ethene has a double bond. The double bond is between two carbon atoms, because hydrogen (H) never has a double bond. H always has a single bond or bond. The double bond is not two sigma bonds, because only two electrons can be in the same space. A double bond contains four electrons in two bonds. The first bond between the two carbon atoms is a sigma bond formed by the overlap of two hybrid orbitals. The second bond between the two carbon atoms is called a pi () bond. The bond is made by the overlap of unhybridized p orbitals. We only make a bond after we have made a bond. The bond is made by the end-to-end overlap of two hybrid orbitals, and the bond is made by the side-by-side overlap of two unhybridized p orbitals. Just as carbon always has four bonds in stable molecules, carbon always has four valence orbitals. Valence orbitals are orbitals that hold valence electrons. Valence electrons are the electrons in the outermost main shell of an atom. A carbon atom has four valence orbitals, three of which hybridize into three sp2-hybrid orbitals when a double bond forms. Figure 7 shows the formation of three sp2 orbitals from a carbon atom.

9

Figure 7. sp2 Hybridization of a Carbon Atom

As always, the hybrid orbitals repel each other and orient as far from each other as possible, in a plane and 120o apart. The remaining unhybridized p orbital is perpendicular to the three hybrid orbitals. Figure 8 shows how a sp2-hybridized carbon forms.

Figure 8. Orbital Arrangement of an sp2-Hybridized Carbon

During hybridization, the number of hybrid orbitals formed equals the number of unhybridized orbitals blended to make the hybrid orbitals. Thus, when we make an sp2 hybridized carbon atom, we make three hybrid orbitals from three unhybridized orbitals. Whether hybridized or unhybridized, carbon always has four valence orbitals.When we change three orbitals into hybrid orbitals, one orbital is not changed. That orbital is a p orbital. The p orbital that is left can overlap side-by-side with a p orbital from another carbon atom and make a pi () bond. Thus, a p + p overlap = bond (p in Greek is ). A bond forms after a bond has formed. In the case of ethene, two carbon atoms are joined by a double bond. First, two sp2 orbitals (each containing one electron) overlap end-to-end to make a sigma bond (sp2 + sp2 orbitals = bond). Then the two p orbitals overlap to make the bond (p + p orbitals = bond). Figure 9 shows the two carbon atoms of ethene making a double bond, one sigma and one pi bond.

10

Figure 9. Overlap of Two sp2-Hybridized Carbon Atoms to Make a Double Bond.

An sp2-hybridized carbon atom has four valence orbitals, three sp2 orbitals and one p orbital. The general principal is that the name of the hybrid orbitals is the same as the name of the hybridized carbon atom. Each orbital contains one electron. Thus, when two sp2 –hybridized carbon atoms form a double bond, we start with eight valence electrons. Two of these electrons, one from each carbon, make a bond. These two electrons, like all electrons, are found in the space on a straight line between the nuclei of the two atoms. Likewise, two electrons make a bond. All six atoms in ethene lie in a plane, so the geometry of a double bond is planar. The bond lies above and below the plane of the six atoms. This leaves four electrons to make bonds with hydrogen. Figure 10 shows the orientation of the bond relative to the plane.

Figure 10. Orientation of Bond

The bond in Figure 10 is shown as a straight line, but actually consists of a space formed by the overlap of an sp2 orbital from one carbon with an sp2 orbital of the other carbon atom. Figure 11 shows the complete bonding orbital picture of ethene.

11

Figure 11. Ethene

Problem 2. What kinds of orbitals overlap to make the carbon-carbon bond in ethene? What kinds of orbitals overlap to make the bond in ethene? What kinds of orbitals overlap to make the carbon-hydrogen bonds in ethene?

Solution 2. Step 1. Draw the structure of ethene.

Step 2. Determine what kinds of bonds ethene has. From the structure, ethene has five bonds and one bond. In stable molecules, carbon always has hybrid orbitals. Step 3. Determine what kinds of hybrid orbitals each of the carbon atoms has? Remember that bonds are made by the overlap of p orbitals. So each carbon atom must have one p (unhybridized) orbital and three hybrid orbitals (carbon always has a total of four bonding orbitals). The three hybrid orbitals must be sp2 orbitals, made by blending the one s atomic orbital with the remaining two p atomic orbitals (i.e. p orbitals that are not used in bonds must be in hybrid orbitals). Step 3. For the carbon-carbon bond, two hybrid orbitals must overlap. Each carbon atom has three sp2-hybrid orbitals. Thus, the bond between the two carbon atoms involves the overlap of an sp2 orbital from one carbon atom with an sp2 orbital of the other carbon atom.Step 4. Pi bonds are always made by the overlap of two p orbitals.Step 5. Each of the carbon-hydrogen bonds involves the overlap of one of carbon’s sp2 orbitals with an s orbital of hydrogen.

Ethyne (Acetylene)Ethyne, which is also known by the common name of acetylene, is shown in the structure below.

Acetylene contains a carbon-carbon triple bond.

12

Problem 3. What kinds of orbitals overlap to make the carbon-carbon bond in acetylene? What kinds of orbitals overlap to make the two bonds in acetylene? What kinds of orbitals overlap to make the carbon-hydrogen bonds in acetylene?

Solution 3. Step 1. Draw the structure of acetylene.

Step 2. From its structure, determine the kinds of bonds acetylene has. The first bond of a multiple bond is a bond and the second and third bonds are bonds. Thus, acetylene has three bonds and two bonds.Step 3. Determine what kind of hybrid orbitals each carbon atom has.Each carbon has two and two bonds. The bonds are made from hybrid orbitals, so each carbon has two orbitals (unhybridized) and two hybrid orbitals, which must be sp orbitals because they are made from the remaining s and p atomic orbitals. Thus, the carbon-carbon bond is made from the overlap of an sp orbital with an sp orbital.Step 4. Pi bonds, including both bonds in acetylene, are always made by the overlap of two p orbitals.Step 5. The carbon-hydrogen bonds are made by the overlap of a hybrid sp orbital with an s orbital.

SummaryOrganic molecules that contain only nonmetals in the structure are covalent molecules. Covalent molecules are held together by covalent bonds. Covalent bonds can be bonds or bonds. The bonds in hydrocarbons can be made between a carbon and hydrogen or between two carbon atoms. The bonds in hydrocarbons must be between two carbon atoms. A covalent bond is a pair of electrons that are found in a three-dimensional space between two atoms. When a bond is formed between two atoms, we can envision that one electron comes from each atom of the pair. These electrons are found in orbitals, either a hybrid orbital (sp, sp2, or sp3) or an unhybridized orbital (s or p). When the bond forms, the orbitals, each containing one electron, come together along the axis joining the atoms in a process that we call orbital overlap. Thus, the two electrons of a bond are located on a straight line between the two atoms, whereas the electrons of a bond are found in a dumbbell or figure-eight shaped space perpendicular to the straight line between the two atoms. The space in which electrons are found is formed by the overlap of an s orbital of an H atom with a hybrid orbital of a carbon atom. Since carbon can have three different kinds of hybrid orbitals, sp, sp2, or sp3, a C-H bond can be made by the overlap of the s orbital of the H atom with an sp, sp2, or sp3 hybrid orbital. The name of the hybridized-carbon atom is the same as the name of its hybrid orbitals. An sp3-hybridized carbon has four sp3 hybrid orbitals; an sp2-hybridized carbon has three sp2 hybrid orbitals and an unhybridized p orbital; and an sp-hybridized carbon atom has two sp orbitals and two unhybridized p orbitals. In molecules, each carbon atom will be hybridized and have a total of four bonding orbitals. In molecules, carbon never has nonbonding valence electrons; all of carbon’s valence electrons are bonding electrons. Thus, a carbon atom that has four bonds is an sp3-hybridized carbon. A carbon atom that is part of one double bond is an sp2-hybridized carbon atom. A carbon atom that is part of two double bonds or one triple bond is an sp-hybridized carbon atom. Hybrid orbitals always repel each other. Thus, two sp-hybrid orbitals orient 180 degrees apart (linear). Three sp2-hybrid orbitals orient 120 degrees apart (trigonal planar). Four sp3-hybrid orbitals orient 109.5 degrees apart (tetrahedral). Because these valence orbitals,

13

occupied by two electrons, repel each other, Pauling originated the name Valence-Shell-Electron-Pair-Repulsion Theory. We use the acronym VSEPR Theory. To find out what kinds of orbitals overlap to make a particular bond, first find the hybridization of the two atoms that make the bond. For a carbon atom, the hybridization gives the name of its hybrid orbitals, and each one of its hybrid orbitals makes a bonds. For hydrogen, there is no hybridization. Hydrogen always overlaps as an unhybridized s orbital. A valence orbital from one atom overlaps with a valence orbital from a second atom to make a bond. Thus, two orbitals are required to overlap to make a space for a pair of electrons.

Complete the following self-quiz and obtain the answers from the instructor.

Self-Quiz 1 Bonding in Organic Molecules

1. How many bonds and bonds are found in cis-2-butene?

2. What kinds of orbitals overlap to make the bond between C-2 and C-3 in cis-2-butene?

3. What kinds of orbitals overlap to make the bond in cis-2-butene?

4. What kinds of orbitals overlap to make a C-H bond at C-1 of cis-2-butene?

5. What kinds of orbitals overlap to make the C-H bond at C-2 of cis-2-butene?

6. What is the hybridization of the C-2 carbon atom in cis-2-butene?

7. What kinds of orbitals overlap to make the bond between C-1 and C-2 in cis-2-butene?

8. What is the hybridization of the C-4 carbon atom in cis-2-butene?

9. What is the geometry around the bond of cis-2-butene?

10. What is the C-1—C-2—C-3 bond angle in cis-2-butene?

Functional Groups and Organic Families

What is a functional group? A functional group is a partial structure, made up of a collection of atoms that are bonded together in a specific manner. Each functional group is associated with a single organic family of compounds. The functional groups subdivide the large number of organic compounds into smaller groups or families. There is a fine line between a group and a functional group. For example, a carbonyl group is found in several organic families such as aldehydes, ketones, acids, esters, and amides. Thus, a carbonyl group is not a true functional group, because it is not associated with a single family. The carbonyl group must be bonded to some other atoms to make unique partial structures that can distinguish the families. Once we understand the functional groups, we can identify them within an organic compound. The members of a family have similar properties. For example, aldehydes are easily oxidized to acids (a chemical property). First semester, we studied several families of organic compounds,

14

including alkanes, alkenes, alkynes, alkyl halides, alcohols, and ethers. This semester we will study aromatic compounds, amines, aldehydes, ketones, acids, and acid derivatives. We will also study some biologically important compounds, including sugars, amino acids, and proteins, which contain multiple functional groups.

During this lab, we will focus on 14 organic families and their functional groups. Since functional groups are partial structures, they must be bonded to other atoms to make a complete organic structure. Thus, the functional groups are shown below with one or more bonds represented by a wavy or squiggly line to show where the other atoms must be bonded. We generally think of a functional group being bonded to an alkyl group. For the most part, you will be asked to identify a functional group or groups in a given structure. You might also be asked to draw the structure of a given functional group. You may also be asked to identify the family or families present in a given structure.

HydrocarbonsOrganic compounds contain carbon. Because carbon must have four bonds, organic compounds must contain some other atoms. Hydrogen is the most common element, other than carbon. You might say that hydrogen just goes along for the ride—like a passenger in an automobile. Thus, hydrocarbons are organic compounds that contain only carbon and hydrogen. Excluding aromatic compounds, there are three organic families that contain only carbon and hydrogen. The presence or absence of multiple bonds distinguishes these families. The hydrocarbon families are shown in Table 1.

Table 1. Hydrocarbon Families and Functional Groups

15

We can think of most organic families as being derivatives of alkanes. That is, we can start with an alkane and remove two hydrogen atoms and get or derive an alkene, etc. The replacement of any hydrogen atom of an alkane by a halogen (i.e., F, Cl, Br, or I) gives an alkyl halide. The word alkyl comes from the word alkane. An alkane has a formula CnH2n + 2. The removal of one H from the formula of an alkane gives an alkyl group of formula CnH2n + 1. Thus, CH4 is methane; the removal of one H gives CH3, a methyl group. Thus, alkyl means alkane minus a H. Replacing the H of an alkane with a halogen gives an alkyl halide. A group similar to halogens is the cyano group. Unlike the halogen atoms, a cyano group contains two atoms, a carbon and nitrogen joined by a triple bond. When the cyano group is joined to an alkyl group, the structure is a member of the nitrile family. Table 2 shows the simple derivatives of alkanes.

Table 2. Alkane Derivatives

Note that the alkane derivatives contain a heteroatom—an atom other than C or H.

Oxygen-Containing Compounds

16

Alcohols and EthersOxygen has a covalence of two, meaning it normally forms two covalent bonds. In

organic families, the two bonds can either be two bonds or one and one (a double bond). Thus, it is convenient to divide oxygen-containing compounds into two groups. One group of compounds contains a carbonyl group, a carbon-oxygen double bond, and the other group does not. The oxygen-containing compounds that do not contain a carbonyl group may be considered as derivatives of water. These compounds are alcohols and ethers. Alcohol and ether families contain oxygen as the only heteroatom and have no multiple bonds. Non-hetero atoms are carbon and hydrogen. Therefore, to make an alcohol, start with a carbon atom and bond an oxygen atom plus hydrogen to it. To make an ether replace the H atom of an alcohol with another C atom. An –OH group is called a hydroxyl group. Alcohols contain a hydroxyl group. Table 3 shows alcohol and ether families.

Table 3. Alcohols and Ethers (One oxygen, no double bond)

Aldehydes and KetonesAldehydes and ketones contain a carbonyl group (C=O) as their only functional feature.

Like alcohols and ethers, they contain only one oxygen atom as the heteroatom. Starting with a carbonyl group and only carbon and hydrogen, we can make aldehydes and ketones. Aldehydes can have an H atom on one or both sides of the carbonyl group, but ketones can only have carbon atoms next to the carbonyl group. Table 4 shows aldehyde and ketone families. An aldehyde must always be a terminal group (i.e., the carbonyl group is at the end of a chain).

Table 4. Aldehydes and Ketones (One oxygen heteroatom in carbonyl)

17

Acids and Acid DerivativesOrganic acids are called carboxylic acids, because they contain a carboxyl group. Joining

a carbonyl group with a hydroxyl group makes a carboxyl group. Like an aldehyde, the functional group must be at the end of a chain. Thus, the acid’s carbonyl group contains carbon atom number one, which has an –OH group bonded to it. In other words, an acid contains two oxygen heteroatoms. This is an important distinction between acids and the oxygen-containing families covered above. A general principal is that acids and acid derivatives contain a carbonyl group with a heteroatom bonded directly to the carbonyl carbon atom. When the H atom of an acid’s hydroxyl group is replaced by an alkyl group, the compound becomes an ester. When a nitrogen atom replaces the oxygen atom of an acid’s hydroxyl group, the compound becomes an amide. These families are shown in Table 5. Table 5. Acids and Acid Derivatives (Two Hetero Atoms, one in a carbonyl)

18

A compound contains a carbonyl group with a chlorine atom bonded to the carbonyl group. Is the compound an alkyl halide or an acid derivative?

Aromatic CompoundsBenzene is an aromatic hydrocarbon. It was originally classified as aromatic because of

its odor, but now aromatic compounds are classified primarily by virtue of the number and arrangement of electrons in the structure. Aromatic compounds were not included in hydrocarbons above, because many aromatic compounds contain heteroatoms. For example, the replacement of a hydrogen atom by a chlorine atom makes an aryl halide, which is an aromatic compound but not a hydrocarbon. When an H atom is removed from benzene, the resulting partial structure is called a phenyl group. When a phenyl group is joined directly to a carboxyl group, we have an aromatic acid. We call compounds that are not aromatic aliphatic. Thus, acetic acid is an aliphatic acid, whereas benzoic acid is an aromatic acid. Table 6 shows some aromatic compounds.

Table 6. Aromatic Compounds

AminesAmines are derivatives of ammonia. Since organic compounds must contain carbon,

amines contain a nitrogen atom bonded directly to a carbon. Unlike amides, which are acid derivatives, amines do not contain a carbonyl group. Carbon atoms may replace one, two or three hydrogen atoms of ammonia. These compounds are called primary, secondary, and tertiary amines, respectively. Table 7 shows amines.

Table 7. Amines

19

Complete the following self-quiz and obtain the answers from the instructor. After you have checked your answers to Self-Quiz 2 and you are ready to take the diagnostic evaluation.

Self-Quiz 2 Families of Organic Compounds

(24E)-3-hydroxy-7,24-euphadien-26-oic acid (Compound 1) is a potential anti-cancer drug that chemists have recently isolated from two different plants.

Compound 1

1. What organic family is found in Compound 1 at C-3?

2. What organic family is found in Compound 1 at C-26?

3. What family is found in Compound 1 at C-7?

4. Draw the structure of a nitrile that has three carbon atoms.

20

5. Draw the structure of a ketone that has three carbon atoms.

6. Draw the structure of an aldehyde that has three carbon atoms.

7. Draw the structure of an amide that has two carbon atoms.

8. The amide of problem 7 is a derivative of what organic acid?

9. Draw the structure of two different esters that have three carbon atoms each.

10. Draw the structure of ethyl alcohol and diethyl ether.

Diagnostic Evaluation

Obtain the diagnostic evaluation from the instructor. You will complete the diagnostic evaluation without the use of notes, etc. and turn it in to the instructor; it is worth 20 points toward your overall lab grade.

21