Chem 150 Unit 2 - Hydrocarbons & Functional Groups

Chem 150 Unit 2 - Hydrocarbons & Functional Groups

Rayat Shikshan Sanstha's S.M. JOSHI COLLEGE, HADAPSAR, PUNE-28 Prof. MADHURI TUPE (Assistant Professor) Department of Chemistry Organic Organic Chemistry Chemistry Organic chemistry is the chemistry of carbon. 2 2 Hydrocarbons Organic molecules contain carbon combined with other elements. Organic molecules are grouped into families Members of a family share common structural, physical, and chemical characteristics. There are four families that contain molecules made of only carbon and hydrogen. Hydrocarbons Alkanes Alkenes Alkynes Aromatics

3 3 Hydrocarbons 4 4 Alkanes Alkanes are hydrocarbons that contain only carbon-carbon single bonds. Every carbon atom participates in 4 single bonds, either to another carbon or to a hydrogen. Every hydrogen atom is bonded to a carbon by a single bond. 5 5 Alkanes Alkanes are hydrocarbons that contain only carbon-carbon single bonds. 6 6 Alkanes Alkanes in which the carbons are connected in a straight chain are called normal alkanes. H H H

H H H H C C C C C C H H H H H H H n-hexane

Alkanes that are branched are called branched chain alkanes. H H C H 7 7 H H H H H C C C C C H H

H H H 2-methyl-pentane H Alkanes For a discusion on the structure of alkanes, see the Unit 2 Elaboration - Alkane Structure Alkanes Alkanes, along with the other hydrocarbons, are non-polar. They interact with each other only through London dispersion forces. This is why they have relatively low boiling and melting points. 9 9 Alkanes They interact with each other only through London dispersion forces. Note how the boiling points increase with molecular weight. 10 10

Alkanes Alkanes, cannot be named based on their molecular formulas For example, all of the molecules shown below share the same molecular formula, C6H14 (hexacarbon tetradecahydride?) H H H H H H H C C C C C C H H

H H H H H n-hexane H H C H H H H H H H H C C C

C C H H H H H H H H H C C H H C H H

H H H H C C C H H H C H H H C C H H C

H H H H C C H H H H H 2-methyl-pentane 11 11 3-methyl-pentane 2,2-dimethylbutane H H

H C C C H H H C H C C H H H H H 2,3-dimethylbutane Alkanes Organic chemists use a systematic set of rules, called the IUPAC rules, to name organic molecules based on their

structural formulas instead of their chemical formulas. H H H H H H H C C C C C C H H H H H

H H n-hexane H H C H H H H H H H H C C C C C H

H H H H H H H H C C H H C H H H H H

H C C C H H H C H H H C C H H C H H H

H C C H H H H H 2-methyl-pentane 12 12 3-methyl-pentane 2,2-dimethylbutane H H H C C C

H H H C H C C H H H H H 2,3-dimethylbutane Constitutional Isomers When two or more molecules share the same molecular formula, but have different atomic connections, they are called constitutional isomers. H H

H H H H H C C C C C C H H H H H H H

n-hexane H H C H H H H H H H H C C C C C H H H

H H H H H H C C H H C H H H H H H C

C C H H H C H H H C C H H C H H H H C

C H H H H H 2-methyl-pentane 13 13 3-methyl-pentane 2,2-dimethylbutane H H H C C C H H H

C H C C H H H H H 2,3-dimethylbutane Conformations Carbon-carbon single bonds are free to rotate This leads to different shapes for some molecules These should 14 14 not be confused with isomers. Conformations All of the 3-dimensional models shown below are for the nbutane.

They were generated by rotating the central carbon-carbon bond. They all share the same structural formula. H 15 15 H H H H C C C C H H H H H

Conformations All of the 3-dimensional models shown below are for the nbutane. They were generated by rotating the central carbon-carbon bond. 16 16 Conformations Switching from one conformation to another does not require the breaking and making of covalent bonds. Switching from one isomer to another does require the breaking and making of covalent bonds. n-butane 2-methylpropane H H 17 17 H H H H

C C C C H H H H H H C H H H H C C C

H H H H Cycloalkanes When there are three or more carbons in a straight chain, the ends can be joined to make rings. In naming these molecules, the prefix cyclo- is used to indicate the ring: Skeletal structural formulas are used to represent the rings in structural formulas: 18 18 Cycloalkanes In naming these molecules, the prefix cyclo- is used to indicate the ring: As Parent Chain As Substituent Group C3H6 cyclopropane R cyclopropyl-

cyclobutane R cyclobutyl- R cyclopentyl- C4H8 C5H10 cyclopentane C6H12 cyclohexane 19 19 R cyclohexyl- Cycloalkanes The carbon-carbon single bonds for the carbons in a ring are no longer free to rotate. This leads to a new type of isomer Since the two structures share the same name, they are not constitutional isomers. CH3 CH3

CH3 1,2-dimethylcyclohexane H H H H 20 20 H H H H CH3 1,2-dimethylcyclohexane H H H CH3 CH3 H CH3 H H H

H H H H CH3 Cycloalkanes Isomers which share the same atomic connections, and therefore, the same IUPAC name are called stereoisomers. When this occurs due to restricted rotation about a covalent bond, they are called geometric isomers The prefix cis- and trans- are used to distinguish geometric isomers. CH3 CH3 CH3 cis-1,2-dimethylcyclohexane H H H H 21

21 H H H H CH3 trans-1,2-dimethylcyclohexane H H H CH3 CH3 H CH3 H H H H H H H CH3

Alkenes, Alkynes & Aromatic Compounds The remaining three families of hydrocarbons are unsaturated. Alkanes are saturated, which means they contain the maximum number of hydrogens per carbon. For alkanes CnH(2n+2) Alkenes, Alkynes and Aromatics are unsaturated, which means they contain less than the maximum number of hydrogens per carbon. 22 22 Structurally, this means that they have carbon-carbon double or triple bonds Alkenes, Alkynes & Aromatic Compounds Alkenes are hydrocarbons that contain at least 1 carboncarbon double bond. Examples: H H C H C H

C H ethene (ethylene) 23 23 H H C CH2 CH2 CH2 CH3 1-hexene Alkenes, Alkynes & Aromatic Compounds Alkynes are hydrocarbons that contain at least 1 carboncarbon triple bond. Examples: H C C H ethyne (acetylene) 24 24

H C C CH2 CH2 CH2 CH3 1-hexyne Alkenes, Alkynes & Aromatic Compounds Aromatics are unsaturated ring molecules They are often drawn to look like alkenes, but they behave much differently than alkenes. They have an alternating pattern of double and single bonds within a ring. Benzene is an example 25 25 Alkenes, Alkynes & Aromatic Compounds The physical properties of all hydrocarbons are the same The have essentially one noncovalent interaction, which isthe London dispersion force. They have no electronegative atoms and therefore have 26 26 No ion/ion interactions

No dipole/dipole interactions No hydrogenbonding interactions Alkenes, Alkynes & Aromatic Compounds Naming of Alkenes and Alkynes work the same as for alkanes, with these added rules: The parent chain must include both carbons in all double and triple bonds. Pick the longest chain that also contains all double and triple bonds The -ene ending is used of alkenes The -yne ending is used for alkynes. The number of the first carbon in the double or triple bond is included in the name to locate the double or triple bond. 27 27 Number the parent chain from the end that is closes to the first double or triple bond. Alkenes, Alkynes & Aromatic Compounds Naming of Aromatics is based on benzene: When the molecule is build on benzene, the parent name is benzene.

There are also many common names used to describe aromatic compounds. 28 28 Alkenes, Alkynes & Aromatic Compounds Naming of Aromatics is based on benzene: Aromatic compounds can contain multiple aromatic rings 29 29 Alkenes, Alkynes & Aromatic Compounds There are many aromatic molecules found in biology Some aromatic compounds contain nitrogen and oxygen atoms For example, the nucleotide base Adenine, which is used to make DNA and RNA NH2 N N N 30 30 Alkenes, Alkynes & Aromatic Compounds Like cycloalkanes, some alkenes can have cis and trans isomers This is due to restricted rotation about the double-bond. Not all double bonds produce cis and trans isomers

Each carbon participating in the double bond must have two different substituents attached to them A X C B C Y A B AND X Y 31 31 Alkenes, Alkynes & Aromatic Compounds Like cycloalkanes, some alkenes can have cis and trans isomers 32 32 Alcohols, Carboxylic Acids & Esters In addition to the four families of hydrocarbons, there are also many other families of organic molecules. These other families include elements other than carbon and hydrogen. They exhibit a wide range of chemical and physical properties.

The families are distinguished by a group of atoms called a functional group 33 33 Alcohols, Carboxylic Acids & Esters Functional Group A functional group is an atom, group of atoms or bond that gives a molecule a particular set of chemical and physical properties 34 34 Alcohols, Carboxylic Acids & Esters The carbon-carbon double bonds found in alkenes is an example of a functional group. A chemical property of a double is that it will absorb hydrogen in the hydrogenation reaction. 35 35 Alcohols, Carboxylic Acids & Esters We look now at three families that are distinguished by a functional group that contains the element oxygen. Alcohols Members of the alcohol family contain a hydroxyl group. The hydroxyl group comprises an oxygen with one single bond to a hydrogen and another single bond to an alkanetype carbon

H H H C C H H O An alkane-type carbon atom ethanol 36 36 H hydroxyl group Alcohols, Carboxylic Acids & Esters We look now at three families that are distinguished by a functional group that contains the element oxygen. Carboxylic acids Members of the carboxylic acid family contain a carboxylic acid group The carboxylic acid group comprises a hydroxyl group connected to a carbonyl group: O C

carbonyl group 37 37 O + O H hydroxyl group C O H carboxylic acid group Alcohols, Carboxylic Acids & Esters Carboxylic acids The present of the hydroxyl group next to the cabonyl group completely changes it properties. The alcohol hydroxyl group and the carboxylic acid hydroxyl group are chemically quite different, which is why molecules that have the carboxylic acid group are placed in a separate family from the alcohols.

Later in the semester we will learn about some of these chemical differences. O C carbonyl group 38 38 O + O H hydroxyl group C O H carboxylic acid group Alcohols, Carboxylic Acids & Esters Carboxylic acids The carboxylic acid group can be attached to a hydrogen, an alkane-type carbon, or an aromatic-type carbon: O

H C OH methanoic acid (formic acid) 39 39 H H H O C C C H H O OH

propanoic acid C OH benzoic acid Alcohols, Carboxylic Acids & Esters We look now at three families that are distinguished by a functional group that contains the element oxygen. Esters Chemically, esters can be synthesized by reacting a carboxylic acid with and alcohol: O C O O H carboxylic acid 40 40 + H O

C alcohol C O C ester + H O H water Alcohols, Carboxylic Acids & Esters We look now at three families that are distinguished by a functional group that contains the element oxygen. Esters Chemically, esters can be synthesize by reacting a carboxylic acid with and alcohol: O CH3 CH2 Carboxylic

acid part C O CH2 CH3 Alcohol part Ethyl propanoate 41 41 Alcohols, Carboxylic Acids & Esters Carboxylic acids The carboxylic acid group can be attached to a hydrogen, an alkane-type carbon, or an aromatic-type carbon: O H C OH methanoic acid (formic acid) 42 42 H

H H O C C C H H O OH propanoic acid C OH benzoic acid Alcohols, Carboxylic Acids & Esters As we saw with the hydrocarbons, the physical properties of organic molecules depend on the noncovalent intermolecular interactions which attract one one molecule to another. With hydrocarbons, there is only one type of noncovalent

interaction: Induced dipole/Induced dipole (London dispersion force) The presence of the electronegative oxygen makes alcohols, carboxylic acids and esters polar molecules, these families, therefore, have at least two types of noncovalent interactions: 43 43 Induced dipole/Induced dipole (London dispersion force) Dipole/Dipole Alcohols, Carboxylic Acids & Esters As we saw with the hydrocarbons, the physical properties of organic molecules depend on the noncovalent intermolecular interactions which attract one one molecule to another. Alcohols and Carboxylic acids also have a hydroxyl group with a hydrogen bonded to an oxygen. This allows them to form hydrogen bonds with each other. Therefore, carboxylic acids have at least three different noncovalent interactions:

44 44 Induced dipole/Induced dipole (London dispersion force) Dipole/Dipole Hydrogen bond Alcohols, Carboxylic Acids & Esters To summarize, the types of noncovalent interact ions that each family can participate in include: Hydrocarbons (Alkanes, Alkenes, Alkynes & Aromatics) Induced dipole/Induced dipole (London dispersion force) Esters Induced dipole/Induced dipole (London dispersion force) Dipole/Dipole Alcohols & Carboxylic acids 45 45 Induced dipole/Induced dipole (London dispersion force) Dipole/Dipole

Hydrogen bond Alcohols, Carboxylic Acids & Esters These interactions are illustrated in Figure 4.23 of your textbook. alcohols esters carboxylic acids 46 46 Alcohols, Carboxylic Acids & Esters Boiling points are a good measure of the strength of the noncovalent interactions between molecules. The stronger the interactions, the higher the boiling point will be. Since all molecules have the London dispersion interaction, the boiling points of molecules is expected to increase with temperature. The next slide shows a chart using the data found in Table 4.7 of Raymond, in which the boiling points for alcohols, carboxylic acids and esters are plotted against molecular weight. 47 47 Alcohols, Carboxylic Acids & Esters

As expected, the boiling points For a given molecular weight, the alcohols and carboxylic acids have a higher boiling point than esters, this is because they can form hydrogen bonds and esters cannot. The carboxylic acids have a slightly higher boiling point than alcohols, because they can form two hydrogen bonds with a neighboring molecule ( See Figure 4.23 in Raymond) 48 48 Boiling Point {C} for members of all three families increases with molecular weight due to the London dispersion interactions. Molecular Weight {g/mol} Alcohols, Carboxylic Acids & Esters Another distinguishing characteristic of many of the families is odor.

You nose is actually a highly sensitive chemical detector. The members of different families can interact differently with the receptors in your nose to produce smells that are characteristic of the families they belong to. For example: 49 49 Carboxylic acids produce the pungent, sometime unpleasant odors associated with ripe cheeses, rancid butter and vomit. Esters, on the other hand, produce the sweet, often pleasant order associated with flowers, perfumes and various natural and artificial flavorings. The next slide shows Figure 4.24 from Raymond, which gives some specific examples. Alcohols, Carboxylic Acids & Esters Examples of some flavorable esters: 50 50 THANK YOU

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