Alkanes: Structure and Properties

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Questions and Answers

What is the general formula of a cycloalkane?

CnH2n-2

CnHn+2

CnHn

CnH2n (correct)

How do you number the ring when there are two substituents on a cycloalkane?

By beginning with the substituent of higher alphabetical order

By alternating between the two substituents

By beginning with the substituent of lower alphabetical order (correct)

Randomly

What is the molecular formula of cyclohexane?

C6H14

C6H16

C6H10

C6H12 (correct)

Why do cycloalkanes contain two fewer hydrogen atoms than an alkane with the same number of carbon atoms?

Because they have a ring structure Signup and view all the answers

What do you do when naming a cycloalkane with only one substituent on the ring?

Do not give the substituent a number Signup and view all the answers

What is the purpose of prefixing the name of the corresponding open-chain hydrocarbon with cyclo- when naming a cycloalkane?

To indicate the presence of a ring Signup and view all the answers

What is the characteristic of alkanes?

Presence of single covalent bonds Signup and view all the answers

Why are alkanes called saturated hydrocarbons?

They contain the maximum number of hydrogen atoms Signup and view all the answers

What is the relationship between molecular size and boiling point of alkanes?

As molecular size increases, boiling point increases Signup and view all the answers

What is the purpose of the IUPAC nomenclature system?

To standardize the naming of organic compounds Signup and view all the answers

How are the prefixes di-, tri-, tetra-, and so on treated in alphabetizing?

They are excluded from alphabetizing Signup and view all the answers

How is a carbon atom classified?

Based on the number of carbon atoms bonded to it Signup and view all the answers

What is the characteristic of butane?

It exists in two structurally different forms Signup and view all the answers

What is the purpose of alphabetizing the names of substituents?

To assign a unique name to each compound Signup and view all the answers

What is the characteristic feature of the alkene structure?

The presence of a carbon-carbon double bond Signup and view all the answers

What type of reactions occur at the carbon-carbon double bond?

Addition reactions Signup and view all the answers

What is the type of bond that is broken during the reaction of the double bond?

Weak π bond Signup and view all the answers

What is the term used to describe the reagents that are seeking a pair of electrons?

Electrophilic reagents Signup and view all the answers

What is the type of reaction in which two molecules combine to yield a single molecule of product?

Addition reaction Signup and view all the answers

What is the term used to describe the loosely held electrons in the π bond?

π electrons Signup and view all the answers

What is the type of reaction that involves the breaking of the π bond and the formation of two strong σ bonds?

Addition reaction Signup and view all the answers

What is the term used to describe the reaction of an alkene with hydrogen in the presence of a catalyst?

Catalytic hydrogenation Signup and view all the answers

What was observed by Vladimir Markovnikov in 1869 regarding the ionic addition of an acid to the carbon-carbon double bond of an alkene?

The orientation of addition follows a pattern where the hydrogen of the acid attaches itself to the carbon atom that already holds the greater number of hydrogens. Signup and view all the answers

Which of the following is a characteristic of Markovnikov's rule?

What is the fate of the carbon atom in the reaction of alkenes with cold, concentrated sulfuric acid?

It gets bonded to oxygen. Signup and view all the answers

What is the correct statement about the reaction of 2-pentene with an acid?

Neither product predominates, and roughly equal quantities of the two isomers are obtained. Signup and view all the answers

Which of the following is NOT a characteristic of the reaction of alkenes with cold, concentrated sulfuric acid?

The reaction always forms two isomeric products in equal quantities. Signup and view all the answers

What is the purpose of Markovnikov's rule?

To predict the major product of an addition reaction. Signup and view all the answers

What is the correct statement about the addition of hydrogen halides to alkenes?

The reaction follows Markovnikov's rule. Signup and view all the answers

What is the main reason why alkynes are insoluble in water?

Their low polarity Signup and view all the answers

What is the primary industrial source of acetylene?

Reaction between calcium oxide and coke Signup and view all the answers

What is the main characteristic of the boiling points of alkynes?

They are very nearly the same as the boiling points of alkanes or alkenes Signup and view all the answers

What is the role of acetyleneases in the biosynthesis of acetylenic fatty acids?

Oxidation of fatty acids with carbon–carbon double bonds Signup and view all the answers

What is the result of dehydrohalogenation of alkyl dihalides?

Formation of a carbon–carbon triple bond Signup and view all the answers

What is the common feature of the reagents used in the preparation of alkenes and alkynes?

They are essentially the same Signup and view all the answers

What is the number of natural products that contain carbon–carbon triple bonds?

More than 1000 Signup and view all the answers

What is the process involved in the biosynthesis of crepenynic acid?

Oxidation of linoleic acid Signup and view all the answers

Study Notes

Alkanes

Alkanes are characterized by only having single covalent bonds.
They are known as saturated hydrocarbons because they contain the maximum number of hydrogen atoms that can bond with the number of carbon atoms present.
The first four alkanes (methane, ethane, propane, and butane) have non-systematic names.
As molecular size increases, so does the boiling point.

Alkane Nomenclature

The nomenclature of alkanes is based on the recommendations of the International Union of Pure and Applied Chemistry (IUPAC).
The number of carbon atoms is reflected in the Greek prefixes for the alkanes containing 5 to 10 carbons.
The prefixes di-, tri-, tetra-, and so on are not included in alphabetizing.
"Iso," as in isopropyl, is included in alphabetizing.

Classification of Carbon and Hydrogen Atoms

Carbon atoms can be classified as primary (1°), secondary (2°), tertiary (3°), or quaternary (4°), depending on the number of carbon atoms bonded to it.

Cycloalkanes

A hydrocarbon that contains carbon atoms joined to form a ring is called a cyclic hydrocarbon.
Cycloalkanes contain two fewer hydrogen atoms than an alkane with the same number of carbon atoms.
The general formula of a cycloalkane is CnH2n.
To name a cycloalkane, prefix the name of the corresponding open-chain hydrocarbon with cyclo-, and name each substituent on the ring.

Alkenes

The characteristic feature of the alkene structure is the carbon-carbon double bond.
The characteristic reactions of an alkene are those that take place at the double bond.
The double bond consists of a strong σ bond and a weak π bond.
The typical reactions of the double bond are of the sort, where the π bond is broken and two strong σ bonds are formed in its place.

Reactions of Alkenes

Addition reactions involve the breaking of the weaker π bond.
Electrophilic reagents are reagents that are seeking a pair of electrons.
The typical reaction of an alkene is electrophilic addition.
Markovnikov's rule states that in the ionic addition of an acid to the carbon-carbon double bond of an alkene, the hydrogen of the acid attaches itself to the carbon atom that already holds the greater number of hydrogens.

Reactions of Alkynes

Physical properties of alkynes are essentially the same as those of alkanes and alkenes.
Alkynes are insoluble in water but quite soluble in the usual organic solvents of low polarity.
They are less dense than water.
Their boiling points show the usual increase with increasing carbon number, and the usual effects of chain-branching.

Alkynes in Nature

More than 1000 natural products contain carbon–carbon triple bonds.
Many alkynes are fatty acids—carboxylic acids with unbranched chains of 12–20 carbon atoms—or are derived from them.

Preparation of Alkynes

A carbon-carbon triple bond is formed in the same way as a double bond: elimination of atoms or groups from two adjacent carbons.
The groups eliminated and the reagents used are essentially the same as in the preparations of alkenes.
Dehydrohalogenation of alkyl dihalides and dehalogenation of tetrahalides are methods of preparing alkynes.

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Description

Learn about the characteristics of alkanes, including their single covalent bonds and maximum hydrogen atoms. Understand their structural isomers and physical properties such as melting and boiling points.