Chem Power Points Chapter 4

These are grouped into families (functional classes) according to the functional group(s) they contain.

These are the family (functional class) with no functional group.

•Each F.G. has specific properties and reactivity.

•Organic compounds that contain the same functional group behave similarly.

Any atom other than carbon and hydrogen

•Common: O, N, S, F, Cl, Br, I

•F.G. is the reactive part of an organic molecule

R is generic – it could be anything.

•Alkenes contain at least one C-C double bond.

• •C atoms in a double bond are closer together than they are in a single bond.
• •Double bonds are stronger than single bonds.

–The second bond is weaker than the first.

–Alkenes are more reactive than alkanes.

An alkene used by the body to produce vitamin A.

–Found in carrots and sweet potatoes

•Fatty acids and cholesterol also contain alkenes.

•C atoms in a triple bond are even closer than they are in a double bond.

• •Triple bonds are stronger than double bonds.
• –Alkynes are even more reactive than alkenes.

•Rare in nature because they are so reactive.

•Poison produced by poison dart frog (histrionicotoxin) contains two alkyne functional groups.

•Aromatic compounds – contain “delocalized” electrons

--Called “aromatic” because many of the first ones discovered had pleasant odors

•Benzene – a simple aromatic compound

• •Appears to have alternating double
• bonds

•We would expect this to be a reactive compound.

•We would expect three bonds to be shorter, three to be longer.

• •In reality, this molecule is very stable.
• –Not very reactive.

•All bonds are equal in length.

•This is because the “double bond” e- are delocalized – they are shared equally by every C-C bond in the molecule.

•Unsaturated cyclic compounds which are unusually stable are said to exhibit aromaticity.

•Arenes – the functional class whose functional group is the benzene ring (sometimes referred to as a phenyl group when it is inside a larger molecule)

•Unreactive group of unsaturated hydrocarbons.

•Polycyclic aromatic hydrocarbons (PAHs) are molecules that contain two or more phenyl groups.

• •Typically formed when organic matter (e.g., leaves) is burned.
• –Tobacco smoke contains several.

–Many have been shown to be carcinogenic.

•Arenes – the functional class whose functional group is the benzene ring (sometimes referred to as a phenyl group when it is inside a larger molecule)

•Unreactive group of unsaturated hydrocarbons.

•Aromatic compounds are also major components of plastics and many types of pharmaceuticals.

•Structural isomers – two or more compounds with the same molecular formula, but different connectivity

•Not all organic compounds are straight chains.

•The simplest alkane that has a structural isomer: C4H10

•Both structures contain 4 C and 10 H, but are connected differently.

•Alkanes that do not have all their carbon atoms connected in a single continuous chain are called branched-chain alkanes.

•Conformational isomers – isomers that differ ONLY by rotation around one or more bonds

•Rotations occur ONLY around single bonds.

•Same connectivity, different arrangements (“conformations”)

•Both structures represent the same molecule

•Structural isomers represent different molecules!

–Different connectivity.

•Conformational isomers represent the same molecule!

–Same connectivity, different appearance.

•An easy way to determine if two compounds are structural or conformational isomers is to systematically name each compound.

• –Structural isomers > different names; they are different molecules.
• –Conformational isomers >same name; same molecule.

1.Find the longest, continuous chain of carbons atoms. This is called the parent chain.

Name the parent chain according to the straight-chain alkane names (methane, ethane, propane, etc.).

3 C à “propane”

2. Identify the groups bonded to the main chain (ignore hydrogen). These are substituents. In the case of branched-chain alkanes, they are called alkyl groups.

Name the alkyl groups according to alkane naming rules, changing the –ane to –yl (methyl, ethyl, propyl, etc.)

3. Number the parent chain starting at the end that puts substituents on carbons with the smallest numbers possible.

List substituents in alphabetical order at the beginning of the name. Separate numbers and words in the name by a dash.

• 3 C à Propane

• Methyl group on carbon #2

2-methylpropane

NOTE: If more than one substituent of the same type is present, indicate this by using the prefixes di-, tri-, and tetra-, but ignore these prefixes when alphabetizing. For example, two methyl groups on a parent chain would be named dimethyl.

2-methylpropane

• 
• butane

Different names > Structural Isomers

•Group 7A elements = Halogens

• •Halogens can be substituents on alkane chains
• –Alkanes with halogen substituents are called haloalkanes or alkyl halides.

• •Halogen substituents: replace –ine with –o.
• –Fluoro, chloro, bromo, iodo, astato

•Rules for naming haloalkanes are the same as those for naming branched-chain alkanes.

•The rules are similar, but not identical, to those for naming branched-chain alkanes.

• 1.The ring serves as the parent name as long as it has more C than any substituent.
• –Remember: Cyclopropane, cyclobutane, cyclopentane, etc.

2.As before, identify the substituents.

3. Number the C in the ring. C 1 will ALWAYS have a substituent.

• 4. Assign numbers to the substituents.
• –On a ring with a single substituent, that subst. is assumed to be on C 1, and the 1 is implied and need not be listed.
• –When more than one subst. is present, number the ring to give the lowest possible subst. numbering.

•Stereoisomers – compounds differing only in the arrangement of their atoms in space

• •C atoms in cycloalkanes form 4 bonds.
• –Structure: Tetrahedral

•One bond in front (out of page)

•One bond behind (into page)

• •Drawing:
• –Bond in front: solid wedge
• –Bond behind: dashed wedge

• •Cycloalkanes: no bond rotation
• –Leads to two distinct sides of the molecule

• Notice the wedge bonds in the ring itself.

•Cis-trans stereoisomers – differ only in the position of two substituents on a ring or double bond

• •Cis- - substituents on the same side
• •Trans- - substituents on opposite sides

Trans-1,2-dimethylcyclopentane


Cis-1,2-dimethylcyclopentane

• •As with cycloalkanes: no bond rotation
• –Leads to two distinct sides of the molecule

•Chiral center – A carbon atom with four different atoms or groups attached to it

• •Enantiomers – nonsuperimposable mirror images of one another
• –Always have at least one chiral center

•Place an asterisk next to the chiral carbon atom(s) in the following compound:

•“Chiral center” = C atom w/ 4 different groups

•More than 1 H? Not chiral.

•C atom w/ 2 methyl groups? Not chiral.

•C with four different groups? Chiral!

• •Different enantiomers have different effects.
• •Chemical receptors have specific shapes

–Only one enantiomer can fit into a given receptor.

–Like trying to put your left-hand into a right-handed baseball glove

•Sometimes, one enantiomer is effective, and the other has no effect.

•L-Dopa

–One enantiomer is used as a Parkinson’s treatment.

–The other has no biological effect.

•Ibuprofen

–Active ingredient in Advil

–Non-steroidal, anti-inflammatory drug (NSAID)

–One enantiomer is active.

–Other enantiomer is converted to the active one by your body

•Sometimes, one enantiomer is beneficial, while the other is harmful.

•Thialidomide

–Anti-morning-sickness drug

–One enantiomer treats morning sickness

• –The other is teratogenic – it causes
• birth defects.

•Drug was originally sold as a 50:50 mixture of both. Many babies were born with shortened arms or legs, and sometimes no limbs at all.