Unit 1 • Functional Groups • Depicting Structures of Organic Compounds • Lewis Structures • Condensed structural formulas • Line angle drawings • 3-dimensional structures • Resonance Structures • Acid-Base Reactions • Curved Arrows
Classes of Organic Compounds • Organic compounds are commonly classified and named based on the type of functional group present. • An atom or group of atoms that influences the way the molecule functions, reacts or behaves. • The center of reactivity in an organic compound
Classes of Organic Compounds • You must be able to recognize and draw the functional groups listed in your syllabus and on the following slides. • Use the following slides and the tables given in the front of your text and in the chapter to learn these.
Alkanes • Contain C-C single bonds • no functional group • Nonpolar covalent bonds • electrons shared equally • Tetrahedral electron domain geometry • sp3 hybridized carbons
Cycloalkanes • Contain C – C with at least 3 of the carbons arranged in a cyclic (ring) structure • No functional group • Nonpolar • Tetrahedral • sp3 hybrid orbitals
Alkenes • Contain C=C (carbon-carbon double bonds) • 1 sigma bond & 1 pi bond • Non-polar • Trigonal planar geometry • sp2 hybridized carbons Which atoms must be coplanar in an alkene?
Alkenes • The C=C present in an alkene is composed of 1 sigma (s) bond and 1 pi (p) bond. • A sigma (s) bond forms when two orbitals overlap end to end. • electron density is centered along the internuclear axis • cylindrically symmetrical Internuclear axis
Alkenes • A pi (p) bond forms when two p orbitals overlap side to side • electron density is located above and below the internuclear axis • oriented parallel to the internuclear axis
Alkenes • Free rotation occurs around single bonds. • Double and triple bonds are rigid. • Cannot rotate freely. • Rotation would cause loss of overlap of the p orbitals, destroying the p bond.
Alkynes • Contain C Ctriple bonds • 1 sigma bond • 2 pi bonds • Nonpolar • Linear electron domain geometry • sp hybridized carbons Which atoms must be co-linear in an alkyne?
Aromatic Ring • Planar ring system with alternating single and double bonds • does not react like an alkene • Nonpolar • Trigonal planar • sp2 hybridized carbons • Benzene ring is a very common aromatic ring.
Alkyl Halides • Contain C-halogen bond • F, Cl, Br, or I • Polar covalent C-halogen bond • electrons shared unequally • Many (but not all) alkyl halides are polar molecules as well.
Polar Covalent Bonds • Two ways to indicate bond polarity • partial charges • d- on more electronegative element • d+ on less electronegative element • direction of dipole moment • + on less electronegative element • arrow pointing toward more electronegative element
Polar Covalent Bonds • Dipole moment: A measure of the separation and magnitude of the positive and negative charges in polar bonds or polar molecules. • Important Polar Covalent Bonds: C-O C-N C-halogen O-H N-H H-halogen • Important Nonpolar Covalent Bonds: C-C C-H halogen-halogen
d- d+ d+ Polar Molecules • Polar Molecule: • a molecule with a non-zero molecular dipole moment • net negative end, net positive end • contains 1 or more polar covalent bonds arranged asymmetrically within the molecule • use molecular geometry to determine polarity • exhibit dipole-dipole interactions • How does the BP of a polar molecule compare to the BP of a nonpolar molecule with similar molar mass?
Nonpolar Molecules • Nonpolar molecules: • a zero (or very small) molecular dipole moment • contain either: • only nonpolar covalent bonds • 2 or more polar covalent bonds arranged symmetrically • London dispersion forces • found in all molecules • only IMF found in nonpolar molecules • strength increases as surface area increases • What variables make SA increase? • What happens to the BP as SA ?
Polar/Nonpolar Molecules Example: Which of the following are polar molecules?
Alcohols • Contain C-O-H bond • hydroxyl group • Polar covalent bonds • C-O bond • O-H bond • Polar molecule • dipole-dipole interactions • hydrogen bonding • What causes hydrogen bonding? • How does hydrogen bonding affect BP?
Ethers • Contain C-O-C bond • Polar covalent bonds • tetrahedrale.d. geometry • bent molecular geo. • Polar molecules • dipole-dipole interactions
primary secondary tertiary Amines • Contain C-N-R R’ • Polar covalent bonds • Polar molecules • Dipole-dipole interactions • Hydrogen bonding (1o and 2o) • Common organic bases • lone pair of e- on N
O C - H Aldehydes • Contain (-CHO) • Carbonyl (C=O) • always on the 1st or last carbon in a chain • trigonal planar geometry • sp2 hybrid orbitals • Polar covalent bond • Polar molecule • dipole-dipole interactions
O C-C-C Ketones • Contain • Carbonyl attached to middle of chain • Polar covalent bond • Polar molecule • dipole-dipole interactions • Trigonal planar e.d. geo. • sp2 hybridized C
Carboxylic Acids • Contain carboxyl group • Polar covalent bonds • Polar molecules • dipole-dipole • hydrogen bonding • trigonal planar • sp2 hybridized carbon
Acid Chloride • Contain • Polar molecule • dipole-dipole forces • Trigonal planar geo. • sp2 hybridized C • Lachrymators
Esters • Contain • Polar covalent bonds • Polar molecules • dipole-dipole interactions • trigonal planar • sp2 hybridized
Amides • Contain • where R and R’ = H or alkyl • Polar covalent bonds • Polar molecules • dipole-dipole interactions • hydrogen bonding (1o and 2o) • C=O is trigonal planar & sp2 hyrbridized
Nitriles • Contain • Polar covalent bond • Polar molecule • dipole-dipole • Linear, sp hybridized C
Functional Groups Example: Identify the functional groups present in the following compounds. testosterone Vanillin Lisinopril
Depicting Structures of Organic Compounds • Organic compounds can be described using a variety of formulas: • Empirical formula • Molecular formula • Lewis structure • Full structural formula • Three dimensional drawings • Condensed structural formula • Line angle drawings
Depicting Structures of Organic Compounds • Ethyl acetate is an organic molecule with: • empirical formula = C2H4O • lowest whole number ratio • molecular formula = C4H8O2 • actual number of each type of atom present
Depicting Structures of Organic Compounds • Ethyl acetate is an organic molecule with: • Lewis structure: • depicts all covalent bonds using a straight line and shows all nonbonding pairs of electrons • What are covalent bonds? • Full structural formula: • a Lewis structure without the nonbonding electrons
Depicting Structures of Organic Compounds • Ethyl acetate is an organic molecule with: • 3-d drawing: • Condensed structural formula • Line angle drawing
Lewis Structures • Lewis structures are used to represent the covalent bonds present in a molecule. • Symbol for each atom • Covalent bonds between atoms depicted using a solid line • Unshared electrons are shown around the appropriate atom
Lewis Structures • To draw a Lewis structure: • Count the number of valence electrons • For a cation (+), subtract 1 electron for each positive charge • NH4+ : 5 + 4 (1) -1 = 8 e- • For an anion (-), add 1 electron for each negative charge • CN-: 4 + 5 + 1 = 10 e-
Lewis Structures • Draw a skeleton structureshowing the chemical symbol for each atom. Connect the appropriate atoms using a single bond. • Skeletons for organic compounds: • The backbone generally contains C-C bonds • N,O, and S can either be part of the backbone or attached to one of the carbons as a substituent. • H will be attached to C,N,S and/or O • Halogens will be attached to C as substituents.
Lewis Structures • Add pairs of electrons to the atoms giving each one an octet • H only gets 2 electrons • Try filling the octets of N, O, S, and halogens first • There will generally NOT be any “leftover” electrons for organic compounds. • Organic ions, however, may have leftover electrons. • Put them on an atom that needs an octet.
N N Lewis Structures • If there are not enough electrons to give all atoms an octet, share electrons to form multiple bonds. • Single bond: • one pair of electrons shared • double bond: • two pairs of electrons shared • triple bond: • three pairs of electrons shared
Lewis Structures Common neutral bonding patterns CNOHHalogens total bonds 4 3 2 1 1 lone pairs 0 1 2 0 3
Lewis Structures Example: Draw the Lewis structure for C2H3I.
Lewis Structures Example: Draw the Lewis structure for a ketone with the molecular formula, C5H9BrO.
Lewis Structures Example: Draw two possible Lewis structures for CH2COCH3-. These two Lewis structures are resonance structures.
Formal Charge • Which atom in each of the previous Lewis structures is negatively charged? • Formal charge provides a method for keeping track of electrons in a compound. • determines which atom(s) in a structure bear(s) the charge in a polyatomic ion • identifies charged atoms within a molecule that is neutral overall.
Formal Charge • Formal charge: • a calculated value that compares the number of valence electrons for a particular atom to the number of electrons assigned to that atom in a Lewis structure • FC = group # - nonbonding e- - 1/2 (bonding e-) -
Positive Neutral Negative C C+ C C - N N+ N N- O O+ O O - Formal Charge Common Organic Bonding Patterns and Formal Charges:
Formal Charge Example: Calculate or determine the formal charge on N and O in (CH3)3NO. All Lewis structures you draw from now on should include any non-zero formal charges that are present.