CHEM 2301 1st EditionExam # 1 Study Guide Lectures: 1 - 8Lecture 1 (January 21)- Almost all reactions involve a molecule that wants to give away electrons interacting with another molecule that wants them.- Drawing Lewis structureso Draw molecular skeletono Count valence electrons o Adjust for chargeo Arrange electrons to fill most shellso Assign formal charges Ways to count electrons:- For octet: Count all electrons around an atom- For formal charge: Count all lone pairs and count one for each bondLecture 2 (January 23)- Shorthand line drawingso Not the same as a Lewis structureo Vertex of two lines indicates that there is a carbon with all four bonds Assume all bonds not shown are to hydrogen atomso Hydrogens must be shown if they are bonded to hetero (non-carbon) atomso Draw in lone pairs and charges if you want to be specifico Must show double bondso A line ending indicates a methyl group - Ring structure namingo Written as cyclo[formula] or by writing out the formula and putting a horizontal bracket over the top of the entire formula- Bond polarity and electronegativityo Direction and magnitude of polarity in bonds is critical for defining reactivityo Atoms with high electronegativies have a stronger attractive force that is exerted upon electrons in covalent bonds Because of this, the electrons will spend more time closer to the nucleus of the atom with the higher electronegativity This causes the more electronegative atom to obtain a partial negative charge and the less electronegative atoms to obtain a partial positive charge- Basic principles of resonance theoryo Resonance structures are not real The real structure is a hybrid of the resonance structureso Resonance structures are not in equilibrium with each other The electrons don’t actually change formso Resonance structures are not isomers They only differ in the arrangement of electrons- Basic principles of resonance theoryo Nuclei don’t differ in position between resonance structures; only electrons moveo Electrons are shifted in lone pairs and multiple bondso Typically shift electrons in pairso Resonance structure is significant when it delocalizes the charge on atoms- Assessing relative importance of resonance structureso Minimize charges (usually less than 2)o Electronegative atoms can have a positive charge if they have a complete octeto Avoid structures with two C atoms of opposite chargesLecture 3 (January 26)- Bonding in organic moleculeso Positive charge on a hetero (non-carbon) atom is not significant in a resonance structure Negative charges are significant Change only one bond per resonance structureo Methane (CH4): All bond angles are 109.5o and are equal lengtho Sp3 hybridization makes a tetrahedral shape Sp2 hybridization makes a trigonal planar shapeo Hybridization orbitals for single (sigma) bonds are in the shape of a dumbbell that is much larger on the side of the atom that is involved in the bond Hybridization only accounts for the number of atoms involved in the bonds, not the number of bonds themselves Double bonds are called pi bonds and are represented with a dumbbell shape (even on both sides) drawn through the center of both atoms in the bondo Atoms in resonance structures that have different hybridizations from one structure to another are actually hybridized in the lowest hybridization that is found for that atom in any of the significant structuresLecture 4 (January 28)- Bronsted-Lowry definitiono Described acidity/basicity in terms of protons A Bronsted-Lowry acid is a proton donor and must contain a proton (H atom) A Bronsted-Lowry base is a proton acceptor and must be able to form a bond to a proton- Must contain a lone pair of electrons or double bond A hydrogen atom with a positive charge (no electron) is considered a proton- Reactions of Bronsted-Lowry acids and bases o A Bronsted-Lowry acid/base reaction results in the transfer of a proton from an acid to a baseo The electron pair of the base forms a new bond to the proton of the acid, forming the conjugate acid of the baseo The acid loses its proton, leaving a lone pair of electrons on the A atom where the bond was. This forms the conjugate base of the acid.- Methanol (CH3OH) and water can act as either an acid or a base- pKa is the measure of the strength of an acido –log(Ka), meaning stronger acids have a lower pKa- Outcome of acid/base reactionso The position of the equilibrium depends on the relative strengths of the acids and baseso Equilibrium always favors formation of the weaker acid and baseo If the pKa of the starting acid is lower than the conjugate acid formed, the equilibrium favors the productsLecture 5 (January 30)- Structural features that influence acidity/basicityo Anything that stabilizes a conjugate base makes the starting acid more acidico Four key factors that affect acidity: Element effects Inductive effects Resonance effects Hybridization effectso Acidity is mostly influenced by the element that the hydrogen is bonded to (determined by electronegativity)o Acidity increases as the size of the group that the proton is bonded to increases (down the columns of the periodic table) Charge density = charge/size Protons are more attracted to the elements toward the tops of the columns because they have a greater charge densityo Hybridization effects A molecule where the central atom has a lower hybridization is the strongest acidLecture 6 (February 2)- Functional groupso Most organic molecules contain a carbon backbone consisting of C-C and C-H bonds to which functional groups are attachedo A functional group is an atom or a group of atoms with characteristic chemical and physical propertieso Structural features of a functional group include: Heteroatoms: atoms other than carbon or hydrogen Pi bonds: most commonly C-C and C-O double bonds- Carbonyl groups (carbon double bonded to oxygen)o Common functional groups with carbonyls Aldehyde, ketone, carboxylic acid, ester, amide- Structure and stereochemistry of alkaneso General formula: CnH2n+2 (where n is an integer)o Properties: hydrophobic, melting and boiling point increase with n and decrease with branching- Classification of H atoms (alkanes)o Primary: bonded to a carbon that is bonded to another carbon; secondary: bonded to a carbon that is bonded to two other carbons; tertiary: bonded to a carbon that is bonded to three other carbons- Newman projection conformationso Eclipsed: