Notes to Supplement Organic Chemistry

Notes to Supplement --- Organic Chemistry

Chemistry I, and AP Chemistry

Mr. von Werder, WLHS

The Element Carbon

► The element carbon has properties that allow it to make up tens thousands of molecules, many of

which are essential to the existence of life.

r  Allotropes of carbon

¦  Allotrope

n  different forms of the same element (as opposed to isotope… or isomer…)

n  due to different bonding patterns or arrangements

n  different forms usually have significantly different chemical and physical properties

¦  Some of the more familiar carbon allotropes:

n  Diamond

·  Each carbon is bonded to four other carbons; tetrahedral geometry (see model)

·  Strong and stable arrangement of the bonds makes diamond very strong and hard.

·  Uses; ornamentation and jewelry, as tips on cutting tools, coatings

n  Graphite

·  Carbon atoms are bonded in sheet-like fashion (see model)

·  ‘Sheets’ are weakly bonded to each other - slip over each other easily (lubricant)

·  Mixture of graphite and clay is used to make pencil “lead”

n  Amorphous carbon

·  Amorphous (“a” – without; “morph” – shape)

·  This form of carbon has no predictable arrangement of its atoms

·  Charcoal, soot, bone black, coke

n  Fullerenes

·  Globe shaped, cage like arrangements of carbon atoms (see model).

·  Also known as “buckyballs” (named geodesic dome engineer R. Buckminster Fuller)

·  Recently discovered (couple of decades ago); uses are still being researched.

r  Unique Bonding of Carbon

¦  Carbon has four outermost (valence) electrons

n  Allows it to typically form four covalent bonds to achieve a stable octet of electrons

¦  Carbons has a relatively small size – its valence electrons are relatively close to the nucleus

n  This small size allows for short strong covalent bonds to form (single, double, triple)

¦  Carbon can form long chains of carbon bonded to carbon, bonded to another carbon, etc.

n  These chains, with other atoms bonded here and there, allow carbon to be the backbone to thousands of different molecules. (Examples…)

Hydrocarbons

► Hydrocarbons – molecules that contain only hydrogen and carbon (surprise).

► These two elements alone can form thousands of different combinations

r  Properties of Hydrocarbons

¦  Two types of bonds exist in hydrocarbons

n  C-C; which is nonpolar

n  C-H; which is essentially nonpolar

n  This means that hydrocarbons as molecules are NONPOLAR MOLECULES

¦  Being nonpolar give hydrocarbons certain properties:

n  Nonconductors of electricity (rubber and plastics are good wire insulators)

n  Low densities (tend to float on water… think of oil slicks, spills, candles)

n  Low melting points, boiling points (tend to liquids and gases at room temp)

n  Do not dissolve well in water (“oil and water don’t mix”; “like dissolves like”)

¦  Find hydrocarbons in places away from possible interaction with oxygen and nitrogen in the air

n  Underground, mostly in deposits of natural gas and petroleum

·  Fossil fuels is a term used because of the theory that they have formed from the compressed, decomposed remains of plants and animals from very long ago

r  Hydrocarbon Structures and Formulas

¦  FORMULAS of hydrocarbons

n  Molecular formula (Review - what was empirical formula?)

·  tells how many of each type of atom in the molecule

·  Examples: C3H8 C6H12 (Review - what are the empirical formulas?)

·  Drawback - no information about the arrangement, or bonding, of the atoms is given

n  Structural formula

·  tells how the atoms in the molecule are bonded to each other, and the types of bonds

·  Examples:

·  Drawbacks - only two-dimensional

- bond angles are not accurately represented

- these can be cumbersome to write out

n  Condensed structural formula

·  does not show each of the C-H bonds, but still usually shows the C-C bonds

·  this avoids some of the hassle of the structural formula, but still shows some bonding

·  Examples:

CH3-CH2-CH3 CH3-CH2-CH2-CH=CH-CH3

·  This is the form that we will use in writing formulas for organic molecules.

n  Carbon skeleton

·  shows only the carbon atoms and their bonds

C—C—C C—C—C—C═C—C

n  Line structure

·  Shows only the bonds between carbons (each bend in the line represents a carbon)

Saturated and Unsaturated Hydrocarbons

r  Naming Hydrocarbon Compounds

n  IUPAC: (International Union of Pure and Applied Chemistry) makes the rules

for naming compounds

n  Memorize the prefixes for hydrocarbon molecules

r  Alkanes

n  Alkanes are hydrocarbons with all single bonds

n  The general formula for any alkane is CnH2n+2

n  What do each of the alkanes have in common?

n  Do you recognize any of these names? How are they used?

n  Saturated hydrocarbons are compounds that contain only

C and H and only single bonds.

n  Straight chain alkanes are simply the compounds listed at right.

n  Branched chain alkanes have carbons that extend off of the main carbon chain (parent chain)

·  substituent group

Ø  branch that occurs off the main chain of carbons

Ø  they “substitute” for a hydrogen

Ø  branches can be more carbons, halogens, or

other groups of atoms

¨  alkyl group is a hydrocarbon substituent (branch)

common ones are to the right

r  Rules for Naming Branched Chain Compounds, given a structural formula

1. Find the longest continuous chain of carbons.

2. Number the carbons (mentally) so branches have lowest numbers.

3. Identify the names of the branches at each position.

4. Use prefixes to indicate more than one of the same branch.

5. List the branches in alphabetical order. (Ignoring prefixes)

Punctuation: , commas separate numbers

- hyphens (dashes) separate numbers and words

Examples:

r  Rules for Writing Structural Formulas, given the name:

1. Write a carbon skeleton based on the root word in the name.

2. Number the carbons (mentally).

3. Attach the substituent groups (branches) to the carbon skeleton at the proper position.

4.  Add hydrogens to each carbon as needed.

Examples:

r  Conformations and Structural Isomers

n  Conformations● just a “different look” at the same molecule

·  On paper it is just the result of writing the structural formula differently.

·  In reality it is due to the rotations of C-C bonds.

·  But, all are the same compound with the same properties… same name.

n  Structural isomers

·  Compounds that have the same molecular formula, but different structural formulas.

·  “iso” – same; “mer” - part

·  For example: C4H10

butane 2-methylpropane

Both have the same molecular formula, but they are different structural formulas.

·  Draw all the possible isomers for C6H14, and then name them.

r  Cycloalkanes

n  Hydrocarbons can also form rings – cycloalkanes

n  Various ring structures are possible, but the most stable are at about five or six carbons

n  Notice that for a ring to form there are two less hydrogens.

n  Naming simple ring structures just requires putting cyclo- as a prefix to the alkane name

n  Note that from a 3-D view, or from a model, that cyclohexane has two possible conformations:

4“boat” - less stable

4“chair” - more stable and found more often in many other organic molecules

r  Unsaturated Hydrocarbons

¦  Unsaturated hydrocarbons – Not filled to capacity with hydrogens

Due to presence of a double or triple bond(s)

¦  ALKANES - organics with all single bonds

-  saturated – filled to capacity with hydrogens

-  have the general formula CnH2n+2

¦  ALKENES - hydrocarbons with one or more double bonds

-  unsaturated – because two hydrogens have to be lost to form the double bond

-  have the general formula CnH2n

-  Naming alkenes: Use the same root name but use an –ene suffix

Number the carbons (mentally); identify where the double bond is

-  Ethene (common: ethylene); used in making plastics

-  Propene (common: propylene); also used in making plastics

-  Note: The double bond prevents rotation around that C=C bond

Allows for another type of isomer – geometric isomer (cis-, trans- forms)

¦  ALKYNES - hydrocarbons with one or more triple bonds

-  unsaturated – also because less than the maximum number of hydrogens

-  have the general formula CnH2n-2

-  Naming alkynes: Use the same root name but use an –yne suffix

Number the carbons (mentally); identify where the triple bond is

(Demo: Flash in the Pan)

-  Ethene (common: acetylene); used in oxyacetylene torches for welding

r  Benzene

n  Benzene is stable arrangement of six carbons in a ring, with 6 hydrogens

n  August Kekule came up with the structure of benzene based on a dream he had…

n  There are 6 electrons are shared equally in the ring of six carbons (delocalized bonding)

·  This delocalized bonding makes the structure more stable and less reactive

·  The circle inside the hexagon better represents the delocalized bonding

·  Often, we just draw the benzene ring (hexagon/circle); the hydrogens are understood.

n  Aromatic compounds – those organic compounds that contain the benzene ring

n  Naming compounds with benzene rings is done two ways:

1. If simple branches come off the benzene ring, “benzene” serves as the root word.

Numbers indicate the position of branches if there is more than one

Disubstituted benzenes – two branches off benzene ring

-  three possible positions for the two branches

-  numbers are the preferred way of designating the branches

-  However, traditionally prefixes of ortho-, meta-, and para- have also been used.

-  Examples: paradichlorobenzene (alternative to naphthalene mothballs)

-  On the lighter side, consider these:

2. If the benzene ring is a branch off a much longer HC chain then we use the prefix “phenyl” to represent the benzene ring.

Polymers

n  Polymer - very large organic compounds formed by adding together many of the same

smaller molecules (monomers)

·  Natural polymers: 4Starch; a polymer made up of glucose monomer units

4Cellulose; a polymer also made of glucose monomer units

(bonded slightly differently than in starch)

4Silk

4Proteins; polymers made up from amino acids as monomers

·  Synthetic polymers: 4Nylon

4Teflon

4Plexiglas; polymethyl methacrylate

4Plastics of various types:

1  PETE

2  HDPE

3  V

4  LDPE

5  PP

6  PS

7  Other

n  Polymerization – the chemical reaction that forms polymers from monomers

·  Addition polymerization

Ø  Monomer often has a double bond

Ø  Reaction is started by splitting one of the bonds in a double bond (usually with heat or a catalyst)

Ø  The unbonded electrons cause a reaction with a neighboring molecule – breaking one of the bonds in its double bond and the reaction continues.

ethylene polyethylene

(ethene)

Ø  (VD:PH Side 10; Ch.23; Polymers) (VD:PH Side 10; Ch.32; Addition Polymers - slime)

·  Condensation polymerization

Ø  Usually two different monomers that react to form the polymer AND the loss of a small molecule (often water). (VD:PH Side 10; Ch.30; Condensation Polymers)

Ø  Amino acids linking together for form proteins are a good example:

Classes of Organic Compounds

Halocarbons, Alcohols, and Ethers

► Hydrocarbons are plentiful, but when you start considering these hydrocarbons with some simple

substitutions there are even more compounds to consider.

► Here we will consider some of the main categories of organic compounds beyond hydrocarbons.

We will learn to recognize each category and learn to name several of them.

Functional Groups – an atom or group of atoms that has a characteristic chemical behavior (function)

r  Halocarbons

¦  One or more of the hydrogens in a hydrocarbon has been replaced by a halogen(s)

¦  Recall: halogens are group 17 on the periodic table (F, Cl, Br. I) X = F, Br, Cl or I

¦  NAMING halocarbons

·  Name the halogens as branches off the main carbon chain

·  The halogens are prefixes (fluoro-, chloro-, bromo-, iodo-) to the hydrocarbon name

·  Use numbers to indicate the halogen position(s)

n  Examples:

¦  Common examples/uses of halocarbons

·  CFCs; chlorofluorocarbons; used as a refrigerants

Ø  Being phased out in some applications; replaced with HFCs; hydrofluorocarbons

·  CCl4; tetrachloromethane (common: carbon tetrachloride);

Ø  Was a dry cleaning solvent (however, toxic and suspected carcinogen)

Ø  Being replaced with dichloromethane

·  DDT; largely used as a pesticide decades ago; but use was banned in the U.S. in 1972

Ø  http://www.chem.ox.ac.uk/mom/ddt/ddt.html

·  Used as intermediates in chemical reactions.

r  Alcohols

¦  One or more of the hydrogens in a hydrocarbon has been replaced by a hydroxyl group (-OH)

¦  Note: the –OH group here does not dissociate in water; so is chemically different than the hydroxide ion (OH-)

¦  The –OH group in alcohols makes them reasonable polar in small molecules (up to 4 carbons), and so they dissolve well in water. (Why not longer chained alcohols?)

¦  NAMING alcohols – we’ll stick to the simple ones.

·  Drop the “e” from the end of the hydrocarbon chain and add “-ol”

·  If necessary, provide the lowest number for the position of the –OH group

n  Examples:

¦  Common examples/uses of alcohols

·  Methanol (common: methyl alcohol)

Ø  Used to “denature” ethanol; “poisons” the ethanol making it unfit to drink. Why do that?

·  Ethanol (common: ethyl alcohol, grain alcohol)

Ø  The “alcohol” in alcoholic beverages – the intoxicating substance

Ø  Naturally produced through fermentation of glucose

·  2-propanol (common: isopropyl alcohol, rubbing alcohol)

Ø  Used as a base for perfumes, creams, lotions, etc.

·  1,2-ethandiol (common: ethylene glycol)

Ø  Used mainly in antifreeze

·  1,2,3-propantriol (common: glycerol)

Ø  Used also as base in soaps, cosmetics, foods, pharmaceuticals…look for it.

r  Ethers

¦  Ether – compound in which an oxygen atom bonded to two carbon atoms

¦  NAMING ethers – I’m not holding you to it.