Chemistry of Carbon
- Abundance and Importance of Carbon
carbon found in all living matter
found in fuels
- Structure and Bonding of Carbon
mostly nonmetallic properties
normal electron configuration v sp3 hybridization
normally shares four electrons which are equal in energy
Figure 20-1 page 625, Orbital models of carbon
double bonds using sp2 hyrbidization
Figure 20-2 page 626 Orbitals for double and triple bonds in carbon
carbon atoms in the same plane for this type of hybridization as in C2H4 and C4H8.
Triple bonds are linear because of the sp hybrid orbitals e.g. C2H2 and C6H10.
- Allotropes of Carbon
Allotropes - definition
hardest material known
most dense form of carbon
extremely high mp (3500oC)
all due to structure
Figure 20-3 page 626 Diamond structure
covalent network crystal
each atom in the center of a tetrahedron
used for cutting, drilling, and grinding
industrial diamonds are not gem quality diamonds
conducts heat better than silver or copper because of its ability to use vibrational motion to transfer the heat
does not conduct electricity because it has no free electrons that can move
feels greasy and crumbles easily
due to structure
figure 20-4 page 627, structure of graphite
layered structure with hexagons in each layer; hexagons involve strong covalent bonds while the layers are held together by weak London dispersion forces and thus can slide over one another
lubricant and lead for pencils
within the layer, each carbon is bonded to only three other carbons and so each has a free electron and so graphite conducts electricity; also the bonds within the layers are resonance hybrids
delocalized electrons - definition
high melting point (3652oC) because the delocalized electrons helps form a strong covalent network within the layers
graphite fibers used in sporting goods; the bonds within layer create a situation that makes it difficult to pull apart the graphite in the direction parallel to the surface of the layers
discovered in 1980
class of compounds; part of the soot that forms when carbon compounds are burned with a limited amount of oxygen
structure is almost spherical cages of carbon atoms; most stable is C60, formed by 60 carbon atoms arranged in interconnected five and six membered rings
figure 20-5 page 628, geodesic dome and fullerenes structure
C60 is called buckminsterfullerenes; structure also resembles a soccer ball
- Organic Compounds
All organic compounds contain some carbon but not all carbon compounds are considered organic e.g. Na2CO3, CO, CO2.
organic compounds - definition
Figure 20-6 page 629 examples of organic compounds
- Carbon Bonding and the diversity or Organic Compounds
carbon electron configuration allows it to form chains and rings; it can also combine with other element, itself, and it can do so using single, double, or triple bonds
- Carbon Carbon Bonding
the bonding that allows carbon to form long chains and rings is called catenation
catenation - definition
not only can you have chains but you can have branched chains and also rings
figure 20-7 page 630 chains v rings
- Carbon Bonding to Other Elements
carbon atoms can bind to elements with similar electronegativities
hydrocarbons - definition
some compounds contain a hydrocarbon backbone and other elements are attached to the backbone; these elements can include O, N, S, and the halogens
Figure 20-8 page 630
- Arrangement of Atoms
Some molecules of carbon can have the same atoms as other molecules of carbon but have different properties because the atoms are arranged differently
e.g. C2H6O can be either ethanol or dimethyl ether
Isomers - definition
The more carbon atoms in a formula, the greater the number of isomers that are possible. e.g. For C8H18 there are 18 isomers; for C9H20 there are 35 isomers; for C10H22 there are 75 isomers.
To distinguish one isomer from another for a particular compound, you need to know more than the molecular formula.
- Structural Formulas
Organic chemists use structural formulas because of things like isomers.
Structural formula - definition
example of structural formula for C4H10 p 630
Figure 20-9 p 631
Condensed structural formula:
Actual three-dimensional appearance of ethanol in figure 20-9
Can have same molecular formula but different structural formula; also can have structural and geometric isomers.
- Structural Isomers
structural isomers - definition
Two structural isomers for the compound C4H10
Butane on the left is a continuous chain of four carbon atoms;
the methylpropane has a continuous chain of three carbon atoms and a methyl group attached to the center carbon.
Structural isomers can have different physical and chemical properties e.g. table 20-1 page 632
- Geometric Isomers
Geometric Isomers - definition
e.g. 1,2-dichloroethene has a cis and trans isomer - page 632
The two chlorines on the same side of the double bond make the left side molecule a cis molecule; when they are on different sides of the double bond they are trans molecules.
The bonding order is the same i.e. each carbon in the double bond is bonded to a hydrogen and a chlorine.
Figure 20-10 p 632
Another example at the bottom of page 632 shows two molecules that are not geometric isomers. Geometric isomers have to have a rigid structure and each carbon has to have two different groups attached
Geometric isomers differ in both physical and chemical properties.
Some geometric isomers are known to differ in physiological behavior e.g. pheromones.
Figure 20-11 page 633 shows the European corn borer.
- Saturated Hydrocarbons
Hydrocarbons are grouped by the type of bonding.
Saturated hydrocarbons - definition
Alkanes - definition
table 20-2 page 635 - Alkanes with one to four carbon atoms
Page 634 homologous series - member differences
Homologous series - definition
Such series have a generalized formula. For the alkanes it is CnH2n+2.
For an alkane with 30 carbons the formula would be C30H62.
Alkanes with four or more carbon atoms can have straight or branched chains and so they can have structural isomers. One to three carbon atoms gives only straight chains and so no structural isomers
Cycloalkanes - definition
Simple form leaves out carbons and hydrogens such as at the top of page 636
When there is a closed chain or ring structure, there are two fewer hydrogens as compared to a similar alkane. e.g. butane and cyclobutane on page 636
The general formula for cycloalkanes is CnH2n.
- Systematic Names of Alkanes
name of longest carbon chain or parent hydrocarbon in the molecule
table 20-3 page 636 - Carbon atom chain prefixes
from five carbons on up, the prefixes are Latin or Greek prefixes
- Unbranched Chain Alkane Nomenclature
Need the prefix to describe the number of carbons in the parent chain; add suffix -ane
e.g. heptane page 636
- Branched Chain Alkane Nomenclature
Alkyl groups - definition
replace suffix -ane of the corresponding alkane with suffix -yl
Table 20-4 page 637
Example - page 637
name groups attached to parent chain
write them in alpha order
use prefix to indicate more than one of a particular group
number where groups attach to parent chain using lowest possible numbers
hyphens separate numbers from names
commas separate numbers
Example p 638
names of alkyl groups and numbering of alkyl group positions on parent chain
alkane nomenclature - page 639
Sample Problem 20-1 page 639
Sample Problem 20-2 page 640
Do practice problems on p 641
- Cycloalkane Nomenclature
One alkyl group attached needs no number to identify its location; if more than one alkyl group, number the carbon atoms in the ring to provide the lowest possible numbers to locate the alkyl groups.
cycloalkane nomenclature p 642
propane example p 642
Examples at bottom of p 642
- Properties and Uses of Alkanes
Table 20-5 p 643
Structure of alkanes: carbon-hydrogen bonds are nonpolar, thus the only forces of attraction are weak intermolecular forces, or London dispersion forces which increases as the mass of a molecule increases.
- Physical States
Table 20-5 p 643
Those with one to four carbons are gases at room temperature.
Natural gas - definition
Larger alkanes are liquids.
Gasoline and kerosene - mostly liquid alkanes. Stronger London dispersion forces because of larger molecules.
Alkanes with a very high molecular mass are solids - even greater London dispersion forces. Paraffin wax.
Figure 20-12 p 643
- Boiling Points
increase with increasing molecular mass
greater molecular mass - greater London dispersion forces
Petroleum - definition
Molecules in petroleum contain from one to more than fifty carbon atoms.
Table 20-6 p 644
Fractional Distillation - definition
Figure 20-13a p 644
Alkanes are less reactive than other hydrocarbons because of their stable single bonds.
They undergo combustion to form carbon dioxide and water.
Greenhouse effect because of carbon dioxide.
Internal combustion engine - knocking caused by spontaneous igniting of fuel before it is reached by the flame front - loss of power. Straight chain HCs are more likely to do this.
Octane rating - definition
Based on mixtures of 2,2,4-trimethylpentane, a highly branched alkane, and heptane, a straight chain alkane.
The term octane comes from the common name of 2,2,4-trimethypentane (isooctane). Pure isooctane is very resistant to knocking and is assigned an octane number of 100. Pure heptane has an octane number of zero and burns with a lot of knocking. Increasing the percentage of branched chain alkanes in gasoline is one way to increase octane rating.
Figure 20-14 p 645 - Octane ratings on gasoline pumps.
- Unsaturated Hydrocarbons
unsaturated hydrocarbons - definition
alkenes - definition
Table 20-7 p 647
simplest has to have two carbons because of double bond
general formula is CnH2n
can have geometric isomers
e.g. butene p 648
- Systematic Names of Alkenes
similar to rules for alkanes
parent chain must contain the double bond
suffix -ene is used with carbon chain prefix
e.g. pentene p 648
number indicating the position of the double bond is placed before the name of the hydrocarbon chain and separated by a hyphen
position and name of alkyl group are placed in front of the double bond position number
If there is more than one double bond, the suffix is as follows: 2 double bonds: -adiene; 3 double bonds: -atriene, etc.
e.g. 1,4-pentadiene p 648
if numbering from both ends gives equivalent positions for the double bonds in an alkene with two double bonds, then the chain is numbered from the end nearest the first alkyl group
e.g. 2-methy,-1,3-butadiene p 648
Alkene Nomenclature p 649
Figure 20-15 p 650
Figure 20-16 p 651
Sample Problem 20-3 p 649
- Properties and Uses of Alkenes
alkynes - definition
simplest one has two carbons
general formula: CnH2n-2
- Systematic Naming of Alkynes
suffix is -yne
similar to alkenes
Alkyne Nomenclature p 651 and Alkyne Nomenclature p 652
1-pentyne and 3-methyl-1-butyne p 652
figure 20-17 p 652
- Properties and Uses of Alkynes
- Aromatic Hydrocarbons
aromatic hydrocarbons - definition
benzene, C6H6 - the primary aromatic hydrocarbon
structure of benzene p 652
not chemically like an alkene
all of the carbon-carbon bonds are the same
molecule is in the same plane
figure 20-18 p 653
condensed form of benzene p 653
simplest aromatic hydrocarbons have one benzene ring as in methylbenzene p 653
- Systematic Names of Aromatic Hydrocarbons
simplest named as alkyl substituted benzenes
alkyl group added to word benzene
No need to specify which carbon of the ring if there is only one alkyl group
If more than one, number the carbons to give all of the alkyl groups the lowest possible numbers
e.g. propylbenzene and 1,3-dimethylbenzene p 653
Simple Aromatic Hydrocarbon Nomenclature p 653 and p654
Sample Problem 20-4 p 654
- Properties and Uses of Aromatic Hydrocarbons
end of notes
An alkyl group is a group of atoms that are formed when one hydrogen atom is removed from an alkane molecule. back
- Alkanes are hydrocarbons that contain only single bonds. back
Allotropes are two or more forms of an element that have different structures. back
fullerenes are dark colored solids made of spherically networked carbon atom cages. back
Delocalized electrons are electrons shred by more than two atoms. back
Organic compounds are covalently bonded compounds containing carbon, excluding carbonates and oxides. back
Catenation is the covalent binding of an element to itself to form chains or rings. back
Hydrocarbons are composed of only carbon and hydrogen; they are the simplest organic compounds. back
Isomers are compounds that have the same molecular formula but different structures. back
A structural formula indicates the number and types of atoms present in a molecule and also sows the bonding arrangement of the atoms. back
Structural isomers are isomers in which the atoms are bonded together in different orders. back
Geometric isomers are isomers in which the order of atom bonding is the same but the arrangement of atoms in space is different. back
Saturated hydrocarbons are hydrocarbons in which each carbon atom in the molecule forms four single covalent bonds with other atoms. back
A homologous series is one in which adjacent members differ by a constant unit. back
Cycloalkanes are alkanes in which the carbon atoms are arranged in a ring, or cyclic structure. back
Alkyl groups are groups of atoms that are formed when on hydrogen atom is removed from an alkane molecule. back
Natural gas is a fossil fuel composed primarily of alkanes containing one to four carbon atoms. back
Petroleum is a complex mixture of different hydrocarbons that varies greatly in composition. back
Fractional distillation involves the separation of the components of a mixture on the basis of boiling points by condensation of vapor in a fractionating column. back
Octane rating of a fuel is a measure of its burning efficiency and its antiknock properties. back
Unsaturated hydrocarbons are hydrocarbons in which not all carbon atoms have four single covalent bonds. back
Alkenes are hydrocarbons that contain double covalent bonds. back
Alkynes are hydrocarbons with triple covalent bonds. back
Aromatic hydrocarbons are hydrocarbons with six membered carbon rings and delocalized electrons. back
Benzene is the primary aromatic hydrocarbon. back