8.3 Structural Representations Flashcards
what are the 3 ways to represent organic compounds
Organic compounds can be represented in a number of different ways: a molecular formula, a structural formula, and a condensed structural formula.
what does a molecular formula do
A molecular formula shows what kinds of atoms are present and how many of each
what does a structural diagram do
A structural diagram (formula) is a two-dimensional representation of the structure of the molecule, using letters for atoms and short dashes for bonds. Bond angles are generally all represented as 90. Hydrogen molecules might be omitted
what does a condensed structural formula do
A condensed structural formula is similar to a molecular formula but shows the structure more clearly. For ethane, the condensed structural formula is CH3CH3. Note that the two methyl groups are shown separately.
what is propane
Propane (C3H8) is gas at room temperature but liquefies under pressure. It is commonly used as fuel for automobiles, stoves, lights and barbecues.
what can groups of atoms around the single carbon-carbon bonds do
Groups of atoms in propane and other alkanes can rotate freely around the single carbon-to-carbon bonds. However, the most stable arrangements are those with the greatest separation between non-bonding atoms.
what is butane
Butane (C4H10) has a boiling point of -0.5C. Like most other alkanes it is used as a fuel, perhaps most commonly in lighters and torches.
after butane how are alkanes named
After butane, the alkanes are named more logically according to the number of carbons. The Greek prefixes “pent-“ (5), “hex-“ (6), “hept-“ (7), “oct-“ (8), “non-“ (9), and “dec-“ (10), precede the ending “-ane.” Thus the names pentane, hexane, heptane, octane, nonane, and decane.
what are mixtures of alkanes used for
Mixtures of alkanes can be used for a variety of functions
Gasoline is pentane + decane
Kerosene is a mix of alkanes with 12-15 carbons
Lubricating oils and greases have from sixteen to twenty-five carbons.
Paraffin waxes have from twenty to thirty.
what happens as the number of carbon atoms in a chain increases
In general, as the number of carbon atoms in the chain increase, the melting and boiling points also increase.
Methane, ethane, propane and butane are all gases at room temperature (25oC) and pressure, but pentane is a liquid because it’s boiling point is above room temperature
what is the general formula for alkanes
The general formula for alkanes is CnH2n+2
what alkanes do you need to know the names of
The first four - methane, ethane, propane, butane - do not use prefixes you are familiar with. The rest, however, do use familiar prefixes (from Unit 3 used in naming molecular compounds) that denote the number of carbon atoms
what types of formulas do alkanes have
Alkanes have molecular formulas and structural formulas. A molecular formula simply counts the numbers of each sort of atom present in the molecule, but tells you nothing about the way they are joined together and so are rarely used in biochem. Structural formulas are tells you how they are joined together.
what are the physical properties of alkanes
Physical Properties
- For carbon chains of one to four C atoms ( C1, C2, C3, C4) the phase at room temperature is gas, for C5to C16is liquid, and for C17and above is solid.
- We will learn later about special hydrocarbons called aromatics which form ring structures.All hydrocarbons which do not form these special ring structures are called aliphatic compounds.All aliphatic substances are nonpolar so they do not dissolve in water. (water is polar, and ¨like dissolves in like¨.)
what are the chemical properties of alkanes
Chemical Properties
- All bonding electrons are occupied so these compounds are said to be saturated. They are thus relatively unreactive at room temperatures making them good lubricators e.g. motor oil, and foundations for plastics.
- At high temperatures, alkanes react vigorously with oxygen to release energy Paraffin wax for candles is an alkane (C25H52). These hydrocarbon undergo combustion reactions making alkanes valuable as fuels.
- Can be broken into smaller units by ¨cracking¨.
- Alkanes undergo SUBSTITUTION reactions, primarily with halogens– replacing a hydrogen with a group VIIA (or group 17) (halogen) atom
