Chapter 17

A particular linear hydrocarbon molecule has six carbons and ten hydrogens. Is it unsaturated or saturated?

Draw the structural formula, showing all \(\mathrm{C}\) and \(\mathrm{H}\) atoms, for 6 -methyl-4-propyl-2octene.

(a) What functional group does the molecule ethanal contain? How can you tell? (b) Draw a dot diagram for the molecule. Answer: (a) The ending -al tells you this molecule is an aldehyde. It therefore contains the aldehyde functional group.

There is no molecule called ethanone. Explain why not.

What are the three known allotropes of carbon? How do their structures differ from one another, and how are they similar?

Explain why a carbon atom almost always forms four covalent bonds in a covalent substance. How is carbon monoxide an exception to this rule?

Consider this incomplete drawing of a threecarbon hydrocarbon: (a) Complete the drawing by adding hydrogen atoms. (b) Complete the drawing by changing one \(C-C\) single bond to \(a C=C\) double bond and then adding hydrogen atoms. (c) Complete the drawing by changing one \(C-C\) single bond to \(a C \equiv C\) triple bond and then adding hydrogen atoms.

A hydrocarbon molecule consists of a chain of four carbon atoms. In this chain there are one \(\mathrm{C}=\mathrm{C}\) double bond and two \(\mathrm{C}-\mathrm{C}\) single bonds. What is the molecular formula? Draw a possible structure.

The geometry about each carbon in a particular hydrocarbon molecule is tetrahedral. What does this say about the possibility of there being \(C=C\) or \(C \equiv C\) bonds in the molecule? Explain.

What is the name of the branch of chemistry devoted to carbon-based molecules? Why is it called this?

Why are there more compounds of carbon than of any other element?

Define the term hydrocarbon.

Draw the structural formula for a linear sixcarbon hydrocarbon that contains only \(C-C\) single bonds. Show all \(\mathrm{H}\) and \(\mathrm{C}\) atoms.

Draw as many different structural formulas as you can of a branched six-carbon hydrocarbon that contains only \(C-C\) single bonds. Show all \(\mathrm{H}\) and \(\mathrm{C}\) atoms.

A particular hydrocarbon molecule possesses a carbon atom bound to three other carbon atoms. (a) What does this tell you about this particular hydrocarbon? (b) Postulate some rules that tell whether a hydrocarbon will be linear or branched depending on the number of other carbon atoms a particular carbon atom is bound to.

Why is it more correct to draw a linear hydrocarbon that contains only \(\mathrm{C}-\mathrm{C}\) single bonds as a zigzag rather than a straight line?

Hydrocarbons are often represented by line drawings. How is it possible to look at a line drawing and deduce the molecular formula of the compound?

Define the terms saturated and unsaturated as applied to hydrocarbons.

A molecule contains 5 carbon atoms and 12 hydrogen atoms. Is it saturated or unsaturated? Explain how you know.

Is the compound \(\mathrm{C}_{7} \mathrm{H}_{14}\) unsaturated or saturated? How can you tell?

Make line drawings for all the isomers of \(\mathrm{C}_{6} \mathrm{H}_{14}\).

In order for two molecules to be isomers, what must be true about their molecular formulas, their structural formulas, and their properties?

Are \(\mathrm{H}_{2} \mathrm{O}\) and \(\mathrm{H}_{2} \mathrm{O}_{2}\) isomers? Explain.

What is wrong with using common names for hydrocarbon molecules?

Relate the words saturated and unsaturated to the general formulas \(\mathrm{C}_{n} \mathrm{H}_{2 n+2} \mathrm{C}_{n} \mathrm{H}_{2 m}\) and \(\mathrm{C}_{n} \mathrm{H}_{2 n-2}\)

What kind of hydrocarbons are called aliphatic and where does the word aliphatic come from?

What endings are added to the root alk- to name hydrocarbons containing all \(\mathrm{C}-\mathrm{C}\) single bonds, hydrocarbons containing one or more \(\mathrm{C}=\mathrm{C}\) double bonds, and hydrocarbons containing one or more \(\mathrm{C} \equiv \mathrm{C}\) triple bonds?

What do the letters in the acronym IUPAC stand for?

What is meant by the expression homologous series? Give an example of one.

How is the general molecular formula for alkenes different from that for alkanes? Explain the basis of this difference.

Name the alkanes that do not use Greek prefixes in their names, and draw the structural formula for each.

The common name for ethyne is acetylene. Draw a dot diagram and a line drawing for this compound, and indicate whether it is more or less unsaturated than ethene.

Define the prefixes meth- eth- prop-and but-. Then draw line diagrams for 5-methyldecane, 5-ethyldecane, 5-propyldecane, and 5-butyldecane.

Is \(\mathrm{C}_{22} \mathrm{H}_{46}\) an alkane, an alkene, or an alkyne? How can you tell?

The IUPAC name for \(\mathrm{C}_{3} \mathrm{H}_{6}\) needs no number in it, but the IUPAC name for \(\mathrm{C}_{4} \mathrm{H}_{8}\) does. Explain.

Do propane, propene, and propyne belong to a homologous series? Explain.

Draw the structural formula and line drawing for 2 -hexene.

What is the relationship between the molecules 2-hexene and 3-hexene? Justify your answer.

Explain why the molecules 1 -hexene, 2 -hexene, and 3 -hexene exist, but the molecules 4 -hexene and 5 -hexene do not.

What should be your first task in naming any hydrocarbon molecule?

Give the molecular formula and line drawing for: (a) propene (b) 1 -octene (c) hexane (d) 2 -butyne (e) 1 -butyne (f) 2,3 -dimethylbutane

Which of the molecules in Problem \(17.72\) represent a pair of isomers? Discuss their differences in terms of bonds and/or linear versus branched.

Where do we start numbering carbons on a main chain when both branches and \(C=C\) or \(C \equiv C\) bonds are present?

Why can't the molecule 2,2 -dimethyl-1-butene exist?

Give the line drawing and molecular formula for: (a) 3 -methylpentane (b) 2,3 -dimethyl-2-butene (c) 3 -methyl-1-pentene (d) 5 -methyl-1-hexyne

Make a line drawing of 5,5 -dimethyl-1-hexene. What would be wrong with calling this compound 2,2 -dimethyl-5-hexene?

True or false? The longest continuous chain of carbons in a hydrocarbon is always the chain to use in naming a hydrocarbon. Explain your answer.

Although it was not discussed in the chapter, it is possible for a hydrocarbon molecule to have more than one site of unsaturation. One such molecule is 1,3 -butadiene; the \(d i\) - tells us there are two double bonds in the molecule. Give the molecular formula and line drawing for this molecule.

The alkanes containing one, two, three, and four carbons are gases at room temperature. However, as alkanes get larger, they become liquids and then solids at room temperature. Why?

Most of gasoline consists of liquid hydrocarbons. If you examine the exhaust pipe of a running automobile you will observe that liquid water continually comes out of it. In addition, a gas is emitted that is known to contribute to the warming of our planet. Explain where the water and the gas come from and what the gas is.