Chapter 22
1
ORGANIC CHEMISTRY - Why So Much Time Studying Carbon?
Carbon forms an almost endless number of compounds because:
a)
carbon can bond to ________ to form long chains. C-C bonds are quite
strong:
BOND DISSOCIATION ENERGIES
Values are in kJ/mol for single bonds except as noted
I
Br
Cl
F
S
O
P
N
Si
C
H
298
366
432
568
347
467
322
391
323
416
436
213
285
327
485
272
234
310
391
582
226
368
213
-
243
193
272
-
201
200
P
184
264
319
490
230
340
209
O
201
204
205
190
-
S
-
213
255
326
226
F
258
238
215
158
Cl
209
217
243
Br
180
193
I
151
H
C
Si
N
366
695 c = o
1076 c / o
264
285
616 c = n
866 c / n
335
301
356
598 c = c
813 c / c
226
160
418 N = N
945 N / N
146
498 o = o
Only H bonds with itself more strongly. Why doesn't H form chains of atoms?
________________________________
b)
carbon forms _______ bonds with a variety of other
nonmetals (H, O, N, S, P, halogens)
c)
carbon compounds of the same formula can often exist with non-identical
structures.
2
CLASSES OF ORGANIC COMPOUNDS
HYDROCARBONS
Compounds containing only _______ and _________. There are three types: alkanes, alkenes,
and alkynes:
type
example
hybridization
of C*
C-C*-C
bond angle
FC of C*
Ox # of C*
alkane
alkene
alkyne
FORMAL CHARGE
For elements that obey the octet rule, the formal charge can be easily calculated from the
equation:
FC = (# of bonds the atom is forming) - (# of bonds the atom was expected to form)
For carbon, the number of bonds expected is always ________.
Calculate the formal charge of each * carbon.
3
OXIDATION NUMBER
Oxidation numbers are assigned based on the following equation:
Ox # = ( # valence electrons before bonding )- ( # valence electrons after bonding)
The number before bonding is found from the ____________ on the Periodic Table. The number
after bonding is found using the following two rules:
a.
bonding electrons belong to the more electronegative atom in the bond
b.
lone pairs belong to the atom on which they reside
Calculate the oxidation numbers of all the * carbons.
ALKANES
An organic compound containing only ____ and _____ with only _____ bonds.
____________ Alkanes are pretty boring compounds because ___________.
reaction
ÄG o 298 K (kJ/mol)
+88
-124
They are unreactive either because thermodynamically they are ____________ or else the
reactions have ______ activation energy because the C-C and C-H bonds are _______.
Alkanes can be __________, _____________, or ___________.
4
NAMES OF SIMPLE ALKANES
number of C
formula
structure
name
1
CH4
methane
2
C2H6
ethane
3
C3H8
propane
4
C4H10
butane
5
C5H12
pentane
6
C6H14
hexane
7
C7H16
heptane
8
C8H18
octane
9
C9H20
nonane
10
C10H22
decane
5
STRUCTURAL ISOMERS
Structural isomers have the same
but
.
To write the formulas for structural isomers, remove one carbon from the “straight chain” alkane
and attach it as a branch to a non-terminal carbon. This reduces the longest continuous chain of
carbon atoms by one. After all possible non-equivalent structures are made, reduce the chain
successively by one carbon until no more isomers are possible.
Example:
Write the line structures for all of the structural isomers of butane
Example:
Write the line structures of all of the structural isomers of pentane.
6
NAMING BRANCHED CHAIN ALKANES
1.
Identify the longest continuous carbon chain. The name of the alkane with that number of
carbons becomes the root or parent name of the compound.
2.
Identify the side groups (substituents) attached to the main chain.
Substituents that are derived from alkanes by removing an H atom are called alkyl groups.
Their name comes from the name of the alkane with the ending -yl.
CH3 --
CH3CH2 --
3.
Number the main chain so that the first group encountered has the lowest number. In
case of tie, use alphabetical priority to decide the direction of numbering.
4.
Write names of groups in alphabetical order. Italicized words not use to alphabetize.
If there are two or more identical groups use prefixes
Use hypens to separate numbers and names of groups.
Use commas to separate numbers.
No hyphen or space between the last named group and the parent alkane...the name is all
one word.
Example: Name all of the structural isomers of butane and pentane
7
FUNCTIONAL GROUPS
When one or more H atoms are removed or replaced with other types of atoms, the molecule
becomes more _________ . The chemical reactions will generally occur at or near the site where
the H’s have been removed or replaced. These sites of increased reactivity are called functional
groups.
molecule
name of functional group
8
Example:
Identify the functional groups in this molecule
The presence of more than one functional group on the same carbon causes a significant
_______in reactivity and the formation of a new functional group. This molecule does _____
contain an alcohol and ketone.
molecule
name of functional group
9
Example:
Identify the functional groups in aspirin.