Chemistry 1027A/B Chapter Notes -Hydrocarbon, Cycloalkane, Chemical Formula

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Topic 2a

Organic Structure #1: Alkanes & Cycloalkanes

 Hydrocarbon: compound that contains only carbon atoms and hydrogen

atoms

What Are Alkanes?

 Alkanes: saturated hydrocarbon whose carbon atoms are arranged in an

open chain

o Contain only carbon-carbon single bonds, maximum number of

hydrogens bonded to it

o Four bonds of each carbon atom are still arranged in a tetrahedral

manner and all bond angles are approximately 109.5°

 Line-Angle Formula: abbreviated way to draw structural formulas in which

each vertex and each line ending represents a C atom and a line

represents a bond

 General formula – CnH2n+2 (end in –ane)

What Is Constitutional Isomerism in Alkanes?

 Constitutional Isomers: compounds with the same molecular formula but a

different order of attachment of their atoms

o These compounds differ in the kind of bonds they have or in their

connectivity

o Different compounds, different physical & chemical properties

o All compounds that have same molecular formula but different

structural formula

 Ability of C atoms to form strong, stable bonds with other C atoms results

in staggering number of constitutional isomers

How Do We Name Alkanes?

 Alkyl Group: group derived by removing a hydrogen from an alkane (R-)

 C atom is classified as 1°, 2°, 3°, or 4° depending of the number of C

atoms bonded to it

 H atom is classified as 1°, 2°, 3° depending on the type of C to which it is

bonded

What Are Cycloalkanes?

 Hydrocarbon that contains C atoms joined to form a ring is called a cyclic

hydrocarbon

 Cycloalkane: saturated hydrocarbon that contains C atoms joined to form

a ring

 Contain two fewer H atoms than alkane with the same number of C atoms

 Five-membered rings and six-membered rings are especially abundant in

biological world

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Document Summary

Hydrocarbon: compound that contains only carbon atoms and hydrogen atoms. Line-angle formula: abbreviated way to draw structural formulas in which each vertex and each line ending represents a c atom and a line represents a bond. General formula cnh2n+2 (end in ane) Ability of c atoms to form strong, stable bonds with other c atoms results in staggering number of constitutional isomers. Alkyl group: group derived by removing a hydrogen from an alkane (r-) C atom is classified as 1 , 2 , 3 , or 4 depending of the number of c atoms bonded to it. H atom is classified as 1 , 2 , 3 depending on the type of c to which it is bonded. Hydrocarbon that contains c atoms joined to form a ring is called a cyclic hydrocarbon. Cycloalkane: saturated hydrocarbon that contains c atoms joined to form a ring. Contain two fewer h atoms than alkane with the same number of c atoms.

Related Questions

a. What is a hydrocarbon ? What is the difference between a saturated hydrocarbon and an unsaturated hydrocarbon ? Distinguish between normal and branched alkane hydrocarbons.

b. What is an alkane ? What is a cyclic alkane ? What are the two general formulas for alkanes ? What is the hybridisation of of carbon atoms in alkanes ? What are the bond angles in alkanes ? Why are cyclopropane and cyclobutane so reactive ?

c. The normal (unbranched) hydrocarbons are often referred to as straight-chain hydrocarbons. What does this name refer to ? Does this mean that the carbons atoms in a straight chain have a linear arrangement ? Explain.

d. In the shorthand notation for cyclic alkanes, the hydrogens are usually omitted. How do you determine the number of hydrogens bonded to each atom in a ring structure ?

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For each of the following, fill in the blank with the correct response. All of these fill-in-the-blank problems pertain to material covered in the sections on alkanes, alkenes and alkynes, aromatic hydrocarbons, and hydrocarbon derivatives.

a. The first "organic" compound to be synthesized in the laboratory, rather than being isolated from nature, was _ _ _ _ _, which was prepared from _ _ _ _ _.

b. An organic compound whose carbon-carbon bonds are all single bonds is said to be _ _ _ _ _.

c. The general orientation of the four pairs of electrons around the carbon atoms in alkanes is _ _ _ _ _.

d. Alkanes in which the carbon atoms form a single unbranched chain are said to be _ _ _ _ _ alkanes.

e. Structural isomerism occurs when two molecules have the same number of each type of atom but exhibit a different arrangement of the _ _ _ _ _ between those atoms.

f. The systematic names of all saturated hydrocarbons have the ending _ _ _ _ _ added to a root name that indicates the number of carbon atoms in the molecule.

g. For branched hydrocarbon, the root name for the hydrocarbon comes from the number of carbon atoms in the _ _ _ _ _ continuous chain in the molecule.

h. The positions of substituents along the hydrocarbon framework of a molecule are indicated by the _ _ _ _ _ of the carbon atom to which the substituents are attached.

i. The major use of alkanes has been in _ _ _ _ _ reactions, as a source of heat and light.

j. With very reactive agents, such as the halogen elements, alkanes undergo _ _ _ _ _ reactions, whereby a new atom replaces one or more hydrogen atoms of the alkane.

k. Alkenes and alkynes are characterized by their ability to undergo rapid, complete _ _ _ _ _ reactions, by which other atoms attach themselves to the carbon atoms of the double or triple bond.

l. Unsaturated fats may be converted to saturated fats by the process of _ _ _ _ _.

m. Benzene is the parent member of the group of hydrocarbons called _ _ _ _ _ hydrocarbons.

n. An atom or group of atoms that imparts new and characteristic properties to an organic molecule is called a _ _ _ _ _ group.

o. A _ _ _ _ _ alcohol is one in which there is only one hydrocarbon group attached to the carbon atom holding the hydroxyl group.

p. The simplest alcohol, methanol, prepared industrially by the hydrogenation of _ _ _ _ _.

q. Ethanol is commonly prepared by the _ _ _ _ _ of certain sugars by yeast.

r. Both aldehydes and ketones contain the _ _ _ _ _ group, but they differ in where this group occurs along the hydrocarbon chain.

s. Aldehydes and ketones can be prepared by _ _ _ _ _ of the corresponding alcohol.

t. Organic acids, which contain the _ _ _ _ _ group, are typically weak acids.

u. The typical sweet-smelling compounds called _ _ _ _ _ result from the condensation reaction of organic acid with an _ _ _ _ _.

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Hydrocarbons are organic molecules that solely consist of hydrogen and carbon atoms. These compounds are considered saturated if they contain the maximum number of hydrogen atoms. Degrees of unsaturation are structural features that cause a compound to have less than the maximum number of hydrogen atoms possible, and cause the hydrocarbon to be considered unsaturated. In hydrocarbons, degrees of unsaturation consist of ring structures and pi bonds (double and triple bonds). The following formulas can be used to determine whether a molecular formula represents an alkane, alkene, or alkyne (assuming that the hydrocarbons are not ring structures, and that the unsaturated compounds only have one double or triple bond).

Alkanes: CnH2n+2

Alkenes: CnH2n

Alkynes: CnH2nâ2

Chemistry 1027A/B Chapter Notes -Hydrocarbon, Cycloalkane, Chemical Formula

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