Organic Chemistry- Chapter 5

Alkenes: Bonding, Nomenclature, and Properties

A molecule containing one or more carbon-carbon double or triple bonds; fewer hydrogen atoms bonded to carbon than in an alkane; contains alkenes, alkynes, and arenes

Unsaturated hydrocarbon

Benzene and its derivatives

Arene

A group derived by the removal of a hydrogen atom from an arene

Aryl group

When the aryl group substituent on a parent chain is a benzene ring, it is called a ______ group

Phenyl

What is the bond angle of an sp² hybridized atom?

120

A C=C bond contains ___ sigma bond and ___ pi bond

One; one

Does any rotation around a C=C bond occur under normal circumstances? Why or why not?

No, because of the presence of the overlapping pi orbitals

In an open chain alkene, are cis or trans isomers more stable? Why or why not?

Trans; there is steric strain present on alkyl substituents on a cis isomer that is not present on the trans isomer

Name the following alkenyl group:

=CH2

Methylene

Name the following alkenyl group:

-CH=CH2

Vinyl

Name the following alkenyl group:

-CH2CH=CH2

Allyl

True or False:

Smaller alkenes are well-known by their common name rather than their IUPAC name

True

In the E,Z naming system, a compound of (E) configuration has high priority groups on ________ side(s)

Opposite

In the E,Z naming system, a compound of (Z) configuration has high priority groups on ________ side(s)

The same

When naming a cycloalkene, the carbon atoms of the ring’s double bond are numbered _ and _ in the direction that gives the substituent encountered first the _______ number

1;2; smaller

True or False:

Cyclopropene-cycloheptene are too small to have trans isomerism

True

Why can’t cyclopropenes-cycloheptenes have trans isomerism?

There would be too much angle strain

True or False:

Cyclooctene and larger ring sizes can experience cis isomerism, but not trans

False

True or False:

Most of the time in alkenes, trans isomerism is more stable than cis, and the same is true with cyclooctene and larger ring sizes

False

For an alkene with n C=C, __ stereoisomers are possible

2^n

When counting C=C to determine the numbers of stereoisomers a compound has, do you count double bonds that are in cycloalkenes smaller than 8? Why or why not?

No, because those double bonds do not show trans isomerism

Alkenes are essentially ________

Nonpolar

What is the only force present in alkenes?

Dispersion forces

Alkenes are _________ in water

Insoluble

Alkenes are _______ in one another, other nonpolar organic molecules, and in ethanol

Soluble

Benzene rings are very ______ and ______

Strong; stable

In organic chemistry I, are benzene ring substituents reactive?

No

List the formula used for finding the Index of Hydrogen Deficiency (degrees of saturation)

(H reference-H molecule)/2

What is the molecular formula of the reference compound when finding the Index of Hydrogen Deficiency?

Cn + H2n+2

Rules pertaining to the Index of Hydrogen Deficiency:

For every halogen present (F, Cl, Br, I)…

Add one additional H

Rules pertaining to the Index of Hydrogen Deficiency:

For group 6 elements (O, S, Se)…

No correction is necessary

Rules pertaining to the Index of Hydrogen Deficiency:

For each atom of Group 5A (N, P, As)…

Subtract one hydrogen

What information does finding the Index of Hydrogen Deficiency give you?

The total number of double bonds/rings present in the molecule

When counting the number of double bonds and rings present in order to determine the Index of Hydrogen Deficiency, do you count double bonds/rings that are smaller than cyclooctene?

Yes

Double bond stability _________ with increasing alkyl substitution

Increases

True or False:

Cis alkenes are more stable than trans alkenes

False

Having both R groups on one carbon of a disubstituted alkene is ____ stable than having an R group on each carbon

More

What degree of substitution is this alkene?

Tetrasubstituted

What degree of substitution is this alkene?

Trisubstituted

What degree of substitution is this alkene?

Disubstituted

What degree of substitution is this alkene?

Monosubstituted

Rank the following from lowest stability to highest stability:

1. Disubstituted alkene

2. Tetrasubstituted alkene

3. Monosubstituted alkene

4. Trisubstituted alkene

3, 1, 4, 2

When naming alkenes, the first carbon of the double bond should have the ________ number possible

Smallest

True or False:

When naming alkenes, giving the C=C a smaller number takes precedence over giving the first substituent the smallest possible number

True

Methylene, vinyl, and allyl are all common _______ groups

Alkenyl

True or False:

Rather than following the same priority rules as the R,S naming system in alkanes, the E,Z system has its own set of priority rules

False

An alkene with two double bonds has what infix?

-adien-

Alkenes containing several double bonds are often referred to as…

Polyenes

In small-ring cycloalkenes, the configuration of the double bond is ___ because such rings are not large enough to accommodate a _____ configuration

Cis; trans

True or False:

Trans configuration in a cycloalkene is only possible if there are 8+ carbons present in the ring

True

In alkenes, melting and boiling points ________ as the number of carbons increases due to _________ surface area

Increase; increased

True of False:

Alkenes have relatively low melting and boiling points

True

Why can an sp² hybridized C accommodate slightly more negative charge than an sp³ hybridized C?

The sp² hybridized C has more s character

The more carbons present in an alkene, the ______ the boiling point

Higher

The higher the surface area of an alkene, the ______ the boiling point

Higher

What is made up of a carboxylic acid with long alkyl groups?

Fatty acid

The building blocks of fats

Fatty acids

List the degree of saturation:

A molecule only containing carbon-carbon single bonds

Saturated

List the degree of saturation:

A molecule containing one carbon-carbon double bond

Monounsaturated

List the degree of saturation:

A molecule that contains at least two carbon-carbon double bonds

Polyunsaturated

In an omega-3 fatty acid, the double bond occurs at the _____ carbon from the ___ of the alkyl group

Third; end

In an omega-6 fatty acid, the double bond occurs at the _____ carbon from the ___ of the alkyl group

Sixth; end

Increasing the number of double bonds in a fatty acid _________ the melting point of the fat

Decreases

The ______ the number of cis double bonds, the ____ kinks in the hydrocarbon chain

Larger; more

What fat is generally a solid at room temperature and contains only single bonds between carbon atoms?

Saturated fat

What fat is generally a liquid at room temperature and has one or more double bonds between carbon atoms?

Unsaturated fat

The process of adding hydrogen atoms to double bonds, thus converting the double bonds to single bonds

Hydrogenation

True or False:

Trans fats in nature are common and cis fats are extremely rare

False

Most trans fats are ___-____, created during the _____________ process

Man-made; hydrogenation

Does a trans or a cis alkene have a slightly higher boiling point?

Cis

Increasing the number of double bonds in the fatty acid _________ the melting point of the fat

Decreases

The more double bonds in a fatty acid, the more kinks. This leads to poor ________ and less van der Waals forces, leading to _____ melting points

Stacking; lower