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Questions and Answers
Which type of strain is primarily associated with the rotation around single bonds in alkanes?
Which type of strain is primarily associated with the rotation around single bonds in alkanes?
What is the correct IUPAC name for a three-carbon alkane?
What is the correct IUPAC name for a three-carbon alkane?
Which conformation type is most stable for butane due to staggered interactions?
Which conformation type is most stable for butane due to staggered interactions?
How are primary, secondary, and tertiary carbons classified in alkanes?
How are primary, secondary, and tertiary carbons classified in alkanes?
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Which of the following statements about alkanes is incorrect?
Which of the following statements about alkanes is incorrect?
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What is the correct suffix for naming alkanes?
What is the correct suffix for naming alkanes?
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In naming a branched alkane, how should you identify the parent chain?
In naming a branched alkane, how should you identify the parent chain?
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When there are two identical substituents on a carbon chain, how should you number them?
When there are two identical substituents on a carbon chain, how should you number them?
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Which prefix indicates the presence of three identical substituents?
Which prefix indicates the presence of three identical substituents?
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What classification describes a carbon atom bonded to three other carbon atoms?
What classification describes a carbon atom bonded to three other carbon atoms?
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Which structure corresponds to the general formula for cycloalkanes?
Which structure corresponds to the general formula for cycloalkanes?
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In which order should substituents be listed when naming a compound with multiple different substituents?
In which order should substituents be listed when naming a compound with multiple different substituents?
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Which term is included in alphabetization when naming alkane substituents?
Which term is included in alphabetization when naming alkane substituents?
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What is the general formula for alkanes?
What is the general formula for alkanes?
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Which of the following describes constitutional isomers?
Which of the following describes constitutional isomers?
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Which prefix in IUPAC nomenclature denotes a 6-carbon alkane?
Which prefix in IUPAC nomenclature denotes a 6-carbon alkane?
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In the context of alkanes, what type of strain is associated with the eclipsing conformations?
In the context of alkanes, what type of strain is associated with the eclipsing conformations?
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What type of carbon is classified as having four distinct substituents?
What type of carbon is classified as having four distinct substituents?
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Which of the following is a correct feature of the line-angle formula in representing alkanes?
Which of the following is a correct feature of the line-angle formula in representing alkanes?
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For an alkane with a 10-carbon chain, what would be its hydrogen count according to the general formula?
For an alkane with a 10-carbon chain, what would be its hydrogen count according to the general formula?
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Which term describes a group derived from an alkane by removing one hydrogen atom?
Which term describes a group derived from an alkane by removing one hydrogen atom?
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An alkane is a saturated hydrocarbon with only carbon-carbon double bonds.
An alkane is a saturated hydrocarbon with only carbon-carbon double bonds.
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The general formula for alkanes is CnH2n.
The general formula for alkanes is CnH2n.
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All carbon atoms in alkanes are sp2 hybridized.
All carbon atoms in alkanes are sp2 hybridized.
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Constitutional isomers have the same molecular formula but different structural connectivity.
Constitutional isomers have the same molecular formula but different structural connectivity.
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The prefix used in IUPAC nomenclature indicates the number of carbon atoms in a molecule.
The prefix used in IUPAC nomenclature indicates the number of carbon atoms in a molecule.
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In the line-angle formula, each line represents a double bond.
In the line-angle formula, each line represents a double bond.
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Aliphatic hydrocarbons are another name for cyclic hydrocarbons.
Aliphatic hydrocarbons are another name for cyclic hydrocarbons.
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The bond angles in alkanes are approximately 109.5°.
The bond angles in alkanes are approximately 109.5°.
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Planar cyclopentane exhibits 12 fully eclipsed C-H bonds, resulting in a torsional strain of approximately 52 kJ/mol.
Planar cyclopentane exhibits 12 fully eclipsed C-H bonds, resulting in a torsional strain of approximately 52 kJ/mol.
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The chair conformation of cyclohexane is more stable than the boat conformation by 27 kJ/mol.
The chair conformation of cyclohexane is more stable than the boat conformation by 27 kJ/mol.
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In a chair conformation, both equatorial and axial C-H bonds are aligned parallel to the imaginary axis of the ring.
In a chair conformation, both equatorial and axial C-H bonds are aligned parallel to the imaginary axis of the ring.
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The angle strain in cyclopentane's envelope conformation is approximately 110°.
The angle strain in cyclopentane's envelope conformation is approximately 110°.
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There are two equivalent chair conformations in cyclohexane that interconvert via a twist conformation.
There are two equivalent chair conformations in cyclohexane that interconvert via a twist conformation.
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Methylcyclohexane has only one stable chair conformation due to the presence of steric strain.
Methylcyclohexane has only one stable chair conformation due to the presence of steric strain.
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Staggered interactions in cyclohexane are eliminated in the boat conformation.
Staggered interactions in cyclohexane are eliminated in the boat conformation.
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All C-H bonds that are axial in one chair conformation become equatorial in the alternative chair conformation of cyclohexane.
All C-H bonds that are axial in one chair conformation become equatorial in the alternative chair conformation of cyclohexane.
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The name of an alkane consists only of a prefix and the suffix -ene.
The name of an alkane consists only of a prefix and the suffix -ene.
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The longest chain of carbon atoms in a branched alkane is referred to as the parent chain.
The longest chain of carbon atoms in a branched alkane is referred to as the parent chain.
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In naming substituents, prefixes such as di-, tri-, and tetra- are included in the alphabetical order.
In naming substituents, prefixes such as di-, tri-, and tetra- are included in the alphabetical order.
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If a cycloalkane has only one substituent, it is necessary to give it a numbering system.
If a cycloalkane has only one substituent, it is necessary to give it a numbering system.
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A carbon bonded to three other carbons is classified as primary.
A carbon bonded to three other carbons is classified as primary.
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The general formula for cycloalkanes is CnH2n.
The general formula for cycloalkanes is CnH2n.
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The number of identical substituents in alkanes can be indicated using the prefixes mono-, di-, and tri-.
The number of identical substituents in alkanes can be indicated using the prefixes mono-, di-, and tri-.
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To number a ring in a cycloalkane with three or more substituents, it should be done to give the lowest set of numbers.
To number a ring in a cycloalkane with three or more substituents, it should be done to give the lowest set of numbers.
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The average density of liquid alkanes is about 1.5 g/mL.
The average density of liquid alkanes is about 1.5 g/mL.
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Oxidation is essential for using alkanes as energy sources.
Oxidation is essential for using alkanes as energy sources.
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Natural gas primarily consists of propane.
Natural gas primarily consists of propane.
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Synthesis gas is a mixture of carbon dioxide and hydrogen.
Synthesis gas is a mixture of carbon dioxide and hydrogen.
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Cis-trans isomers can be interconverted by rotation about sigma bonds.
Cis-trans isomers can be interconverted by rotation about sigma bonds.
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Methanol can be produced from synthesis gas.
Methanol can be produced from synthesis gas.
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Cyclopentane is often viewed through an edge or from above.
Cyclopentane is often viewed through an edge or from above.
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For trans-1,4-dimethylcyclohexane, the diaxial chair conformation is more stable than the diequatorial chair conformation.
For trans-1,4-dimethylcyclohexane, the diaxial chair conformation is more stable than the diequatorial chair conformation.
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High-molecular-weight alkanes (18 or more carbons) are typically liquids at room temperature.
High-molecular-weight alkanes (18 or more carbons) are typically liquids at room temperature.
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Cis-1,4-dimethylcyclohexane has alternative chairs that are of equal stability.
Cis-1,4-dimethylcyclohexane has alternative chairs that are of equal stability.
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Dispersion forces are weak intermolecular forces present in polar compounds.
Dispersion forces are weak intermolecular forces present in polar compounds.
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Low-molecular-weight alkanes are gases at room temperature.
Low-molecular-weight alkanes are gases at room temperature.
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Cyclohexane is commonly represented as a planar hexagon when viewed from the side.
Cyclohexane is commonly represented as a planar hexagon when viewed from the side.
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The Eclipsed conformation of a carbon-carbon single bond is characterized by the atoms on one carbon being as far apart as possible from the atoms on an adjacent carbon.
The Eclipsed conformation of a carbon-carbon single bond is characterized by the atoms on one carbon being as far apart as possible from the atoms on an adjacent carbon.
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Torsional strain is the strain that occurs when nonbonded atoms separated by three bonds are forced into a staggered arrangement.
Torsional strain is the strain that occurs when nonbonded atoms separated by three bonds are forced into a staggered arrangement.
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Cyclopentane exhibits significant angle strain due to its bond angles deviating from the tetrahedral angle.
Cyclopentane exhibits significant angle strain due to its bond angles deviating from the tetrahedral angle.
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The lowest energy conformation for an alkane is the eclipsed conformation.
The lowest energy conformation for an alkane is the eclipsed conformation.
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The IUPAC naming system includes a prefix indicating the number of carbon atoms in the parent compound.
The IUPAC naming system includes a prefix indicating the number of carbon atoms in the parent compound.
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The term 'butanol' corresponds to butan-1-ol, indicating that it is an alcohol compound.
The term 'butanol' corresponds to butan-1-ol, indicating that it is an alcohol compound.
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Staggered conformation achieves the highest energy state due to maximum interaction between nonbonded atoms.
Staggered conformation achieves the highest energy state due to maximum interaction between nonbonded atoms.
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The IUPAC name 'ethyne' indicates that the compound contains a triple bond between carbon atoms.
The IUPAC name 'ethyne' indicates that the compound contains a triple bond between carbon atoms.
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Study Notes
Alkanes and Cycloalkanes
- Hydrocarbon: A compound made up of only carbon and hydrogen.
- Saturated hydrocarbon: A hydrocarbon with only single carbon-carbon bonds.
- Alkane: A saturated hydrocarbon with carbon atoms arranged in an open chain.
- Aliphatic hydrocarbon: Another name for an alkane.
Structure of Alkanes
- Shape: Tetrahedral geometry (all carbons are sp³ hybridized). All bond angles are approximately 109.5°.
Representing Alkanes
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Line-angle formula: An abbreviated way to draw structural formulas.
- Each line represents a single bond.
- Each line ending represents a CH₃ group.
- Each vertex (angle) represents a carbon atom.
Alkanes - General Formula
- Alkanes have the general formula CₙH₂ₙ₊₂
Constitutional Isomers
- Constitutional isomers: Compounds with the same molecular formula but different connectivity of their atoms.
IUPAC Nomenclature
- Suffix -ane: Specifies an alkane.
- Prefix: Tells the number of carbon atoms.
IUPAC Nomenclature (continued)
- Parent name: The longest carbon chain.
-
Substituent: A group bonded to the parent chain.
- Alkyl group: A substituent derived by removing a hydrogen from an alkane; given the symbol R⁻. CH₄ becomes CH₃⁻ (methyl).
IUPAC Nomenclature (continued)
- Listing substituents:
-If there is one substituent, number the chain from the end that gives it the lower number.
- If there are two or more identical substituents, number the parent chain from the end that gives the lower number to the substituent encountered first. The number of times a substituent occurs is indicated by di-, tri-, tetra-, and so on.
- If there are two or more different substituents, list the substituents in alphabetical order. Number from the end of the longest chain that gives the substituent encountered first, the lower number. The prefixes (di, tri, tetra) are not included in alphabetical order. "Iso" (as in isopropyl) is included in alphabetizing.
Classification of Carbons
- Primary (1°): A carbon bonded to one other carbon.
- Secondary (2°): A carbon bonded to two other carbons.
- Tertiary (3°): A carbon bonded to three other carbons.
- Quaternary (4°): A carbon bonded to four other carbons.
Cycloalkanes
- General formula: CₙH₂ₙ
- Five- and six-membered rings are most common.
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Structure and nomenclature:
- Prefix the name of the corresponding open-chain alkane with "cyclo-".
- Give a name and number to each substituent on the ring. -If only one substituent needs to be named, no need to number. -If two substituents need a number, number the ring from the substituent of lowest alphabetical order. -If three or more substituents are present, number to get the lowest set of numbers, and then list them alphabetically.
Cycloalkanes (continued)
- Commonly written as line-angle formulas: Examples include isopropylcyclopentane, 1-tert-Butyl-4-methyl-cyclohexane, 1-Isobutyl-2-methyl-cyclohexane, 1-Ethyl-1-methyl-cyclopropane.
IUPAC- a general system
-
prefix-infix-suffix
- Prefix: Tells the number of carbon atoms in the parent.
- Infix: Tells the nature of the carbon-carbon bonds.
- Suffix: Tells the class of the compound.
IUPAC - a general system (continued)
- Examples: propene, ethanol, butanone, butanal, butanoic acid, cyclohexanol, ethyne, ethanamine.
Conformation
- Conformation: Any three-dimensional arrangement of atoms in a molecule that results from rotation about a single bond.
- Staggered conformation: A conformation about a carbon-carbon single bond where the atoms on one carbon are as far apart as possible from the atoms on an adjacent carbon.
- Eclipsed conformation: A conformation about a carbon-carbon single bond where the atoms on one carbon are as close as possible to the atoms on an adjacent carbon.
- Torsional strain: Strain that arises when nonbonded atoms separated by three bonds are forced from a staggered conformation to an eclipsed conformation, also called eclipsed interaction strain.
- The lowest energy conformation of an alkane is a fully staggered conformation.
Cycloalkanes (cont'd)
- Cyclopentane: In planar cyclopentane, all C-C-C bond angles are 108°, slightly different from the tetrahedral angle of 109.5°. Consequently, there is little angle strain.
- Angle strain: Strain that arises when a bond angle is either compressed or expanded compared with its optimal value.
- Cyclopentane (cont'd): In planar cyclopentane, there are 10 fully eclipsed C-H bonds. Puckering to an "envelope" conformation relieves part of this strain.
Cyclohexane
- Chair conformation: The most stable conformation of cyclohexane. In a chair conformation, all bond angles are approximately 109.5°, and all bonds on adjacent carbons are staggered.
- Chair cyclohexane: Six C-H bonds are equatorial, and six are axial.
- Equatorial bond: Extends from the ring roughly perpendicular to the imaginary axis of the ring.
- Axial bond: Extends from the ring roughly parallel to the imaginary axis of the ring.
- Boat conformation: A puckered conformation in which carbons 1 and 4 are bent toward each other. A boat conformation is less stable than a chair conformation by 27 kJ/mol (6.5 kcal/mol).
- Torsional strain: Created by four sets of eclipsed hydrogen interactions.
- Steric strain: Created by one set of flagpole interactions.
Cyclohexane (continued)
- Examples of commonly written line-angle formulas: isopropylcyclopentane, 1-tert-butyl-4-methyl-cyclohexane, 1-isobutyl-2-methyl-cyclohexane, 1-ethyl-1-methyl-cyclopropane
Cis-trans isomerism
- Cis-trans isomers: Have the same molecular formula and the same connectivity of atoms but different arrangements of atoms in space that cannot be interconverted by rotation about sigma bonds.
-
Cyclopentane: A cyclopentane ring is commonly viewed through an edge or from above.
- Examples: cis-1,2-dimethylcyclopentane, trans-1,2-dimethylcyclopentane.
-
Cyclohexane: A cyclohexane ring is commonly viewed as a planar hexagon viewed from the side or from above.
- Examples: cis-1,4-dimethylcyclohexane, trans-1,4-dimethylcyclohexane.
Cis-trans isomerism (continued)
- In viewing chair conformations, groups equatorial in one chair are axial in the alternative chair.
- For trans-1,4-dimethylcyclohexane, the diequatorial chair is more stable than the diaxial chair.
- For cis-1,4-dimethylcyclohexane, the alternative chairs are of equal stability.
Physical Properties
- Alkanes are nonpolar compounds and have only weak interactions between their molecules.
- Dispersion forces: Weak intermolecular forces of attraction resulting from temporary induced dipoles.
- Boiling point: Low-molecular-weight alkanes are gases, higher-molecular-weight alkanes are liquids, and high-molecular-weight alkanes are solids.
- Density: Alkanes have an average density of about 0.7 g/mL, and liquid and solid alkanes float on water.
- Constitutional isomers: Different compounds with different physical properties.
Reactions of Alkanes
- Oxidation: The basis for using alkanes as energy sources for heat and power.
- Heat of combustion: The heat released when one mole of a substance is oxidized to carbon dioxide and water.
Sources of Alkanes
- Natural gas: Primarily methane, with some ethane.
- Petroleum: Gasses, naphthas, kerosene, fuel oil, lubricating oils, and asphalt.
- Coal: A source for synthesis gas, which is a mixture of carbon monoxide and hydrogen.
Synthesis Gas
- Synthesis gas: A mixture of carbon monoxide and hydrogen in varying proportions.
Methane Economy
- If the United States moves from a petroleum economy to a natural gas economy, synthesis gas and synthesis gas-derived methanol will be key building blocks.
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Description
Test your knowledge on alkanes, including their structural characteristics and proper nomenclature. This quiz covers topics such as conformation stability, classification of carbons, and IUPAC naming rules. Perfect for students studying organic chemistry or hydrocarbon compounds!
