Chem 340 Study Guide 1
Chem 340 Study Guide 1 Chemistry 340
Popular in Organic Chemistry
Popular in Organic Chemistry
This 3 page Study Guide was uploaded by Leslie Pike on Tuesday September 6, 2016. The Study Guide belongs to Chemistry 340 at Western Kentucky University taught by Rathnayake in Winter 2016. Since its upload, it has received 41 views. For similar materials see Organic Chemistry in Organic Chemistry at Western Kentucky University.
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Date Created: 09/06/16
Organic chemistry is the chemistry of compounds containing carbon. In 1828, Friedrich Wohler disproved the theory of vitalism, that only living organisms could produce organic compounds, when he synthesized urea. Salts vs. Molecules Salts contain ionic bonds, where one atom is much more electronegative (difference greater than 1.5) than the other and it takes both electrons. Most organic compounds (aka molecules) instead have covalent bonds, where both atoms share the electron pair. Some organic compounds have polar covalent bonds, 0.5 < EN difference < 1.5, where the electrons are shared unequally. Isomers Structural isomers (or constitutional isomers) have the same chemical formula but different connectivity. Example: an ester and an alcohol have the same number of atoms but one has the oxygen in the middle of the molecule bonded to two carbons, and the other has at the end bonded to a carbon and a hydrogen. Stereoisomers: same connectivity but not identical molecules. Example: cis-trans isomers Rules for drawing Lewis structures 1. Use only valence electrons. Add up the total number of valence electrons, add (or subtract) extra electrons if the molecule has a negative or positive charge, and that is all of the electrons that you have available to use. 2. Try to give each atom a full octet. Only atoms in the third period and below (phosphorous, sulfur, etc.) can have more than 4 bonds. NO TEXAS CARBONS! 3. Minimize formal charge. DO NOT put a positive charge on one atom and a negative charge on another in the same molecule; the molecule should have only positive charges or only negative charges. 4. More bonds = more stable structure = preferred 5. When drawing three-dimensional structures, wedge means coming out of the page, and dashes mean going into the page. Wedge and dash must be next to each other, not on opposite sides of the molecule. A resonance structure exists when more than one bond arrangement is possible. Example: carbonate has one carbon atom bonded to three oxygen atoms. A Lewis structure shows that two are sigma-bonded, and one is pi-bonded. Any of the three oxygens could have the pi bond. However, actual analysis of carbonate shows that the “pi bond” is spread across the whole molecule, instead of existing between two atoms. This delocalization of electrons is known as resonance. Bonding vs. antibonding orbitals An electron is a three-dimensional wave. When two electrons form a bond, they add. If they are in phase, they form a bonding orbital. (Adding two waves in phase amplifies the wave.) If they are out of phase, they form an antibonding orbital. (Adding two waves out of phase cancels them.) The diagrams on pages 29-39 of the textbook do a good job illustrating this. (I’m not allowed to include them in these notes because of copyright laws, but you can look them up in your book.) Hydrocarbon groups An alkane contains only sigma bonds. An alkene contains at least one double bond. An alkyne contains at least one triple bond. All three of these are hydrocarbons, they contain C and H only. Functional groups Methyl: CH 3 Ethyl: C2H5— Propyl: C3H7— Butyl: C4H9— Phenyl: benzene ring attached to R group Benzyl: Benzene ring with one carbon between it and the R group Alcohol: --OH Amine: --NH 3 Ether: --C—O—C— Carbonyl: C==O (Dr. Hill is not looking for this) Aldehyde: carbonyl bonded to H and R Ketone: carbonyl bonded to R and R Carboxylic acid: carbonyl bonded to R and OH Ester: carbonyl bonded to R and OR Amide: amine bonded to one carbonyl and two R groups (these R groups can be hydrogens) Nitrile: C triple bonded to N Primary, secondary, and tertiary For alkyl halides and alcohols: o A primary alkyl halide (or alcohol) has one carbon and two hydrogens bonded to the carbon that has the halide or OH o A secondary alkyl halide (or alcohol) has two carbons and one hydrogens on said carbon o A tertiary alkyl halide (or alcohol) has three carbons and zero hydrogens on said carbon For amines: o A primary amine has one carbon and two hydrogens bonded to nitrogen o A secondary amine has two carbons and one hydrogen bonded to nitrogen o A tertiary amine has three carbons and no hydrogens bonded to nitrogen Intermolecular forces (larger force = higher boiling point) Dipole-dipole: molecule must be polar (acetone, formaldehyde, water, etc.) the positive end of one molecule draws the negative end of another molecule. Hydrogen bond: a stronger dipole-dipole, must have hydrogen bonded to nitrogen or oxygen Dispersion: all molecules have this, the larger the molecule the stronger the force. Helium has the lowest boiling point of all molecules because it is a small, single atom and thus has no dipole forces and extremely low dispersion forces.
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