Welcome To Honors Organic Chemistry About me What

Welcome To Honors Organic Chemistry!

About me…

What about you…? Interests? Hobbies? Proposed major? Chemistry? Biology? Healthcare? What do you hope to gain from taking this course and/or why are you taking this course?

Structure & Bonding: Course Standards OCHEM. PS 1: MATTER & ITS INTERACTIONS 1) Construct chemical compounds as condensed models, line structures & skeleton models of covalently bonded organic compounds. 2) Develop & use models for structural isomers of organic compounds and advanced resonance hybrid systems. 3) Analyze possible isomers & determine the most probable structure of organic compounds by computation of formal charge. OCHEM. PS 2: MOTION & STABILITY: FORCES & INTERACTIONS 1) Develop & use models including fishhook & curved arrows to represent the movement of electrons in reactions and resonance structures.

Structure & Bonding What is organic chemistry? Why is carbon unique? How is organic chemistry used and why is it important? Three examples of organic molecules – models… Methane CH 4 – simplest of all organic compounds. Combustible? Produced by anaerobic (? ) decomposition. Propanol C 3 H 7 OH – rubbing alcohol used to sanitize surfaces and sterilize wounds. Other alcohols? Trichlorofluorocarbons – (? ) contain carbons and several halogens. Used as aerosol propellants and refrigerants.

Structure & Bonding Complicated organic compounds contain many carbon atoms. Organic chemists have devised a shorthand to draw structural formulae. Solid lines represent a two-electron chemical bond. (? ) When no atom is drawn at the corner of a ring, organic chemists assume carbon. What do the double lines represent? How many electrons?

Structure & Bonding Some examples of important organic molecules…

Structure & Bonding Common features of organic compounds: Organic compounds contain carbon atoms & most contain hydrogen atoms. Carbon atoms have four bonds and stable carbon atoms are said to be “tetravalent” (? ). Other elements may be present including N, O, S, P and halogens. Some have chain structures and others have ring structures - both of which have varying chemical properties (? ). Hence, there are COUNTLESS organic compounds. Carbon forms four strong bonds with itself and other elements. Carbon atoms combine to form rings and chains.

Structure & Bonding Research Ginkgolide B Chemical formula? Applications? Source? History? Structural formula? Information about its structural formula? Controversy concerning medicinal efficacy?

Structure & Bonding A Review… All matter is composed of the same building blocks called ________. The two main components are the _______ and the ___________. Protons? Neutrons? Electrostatic charge? Neutral atoms vs ions vs isotopes? Cations? Anions? Atomic number vs mass number?

Elements in the same row are similar in size. Elements in the same column have similar electronic & chemical properties.

Structure & Bonding More than 115 elements exist - however, most are not common in organic compounds. Most elements commonly found in organic compounds are located in the first and second rows of the periodic table. WHY? Discuss atomic structure…electrons are added to a shell of orbitals around the nucleus. Which electron shells are lowest in energy? Highest? Which electrons are held most tightly to the nucleus? What are the four different kinds of orbitals? (think letters! ) Why are these “letters” unique? What do the different letters mean? In terms of relative energy, rank the orbitals lowest to highest.

Structure & Bonding Remember? ! – Elements in the first row can only have a maximum of two electrons. What about elements in the second row? Discuss… What are the shapes of the electron clouds?

POP QUIZ!!! While the most common isotope of nitrogen has a mass number of 14 (nitrogen-14), a radioactive isotope of nitrogen has a mass number of 13 (nitrogen-13). Nitrogen-13 is used in PET (positron emission tomography) scans by physicians to monitor brain activity and diagnose dementia. For each isotope, give the following information: (a) the number of protons; (b) the number of neutrons; ( c ) the number of electrons in the neutral atom; and (d) the group number. Propose an hypothesis as to why N-13 is radioactive – as opposed to its more stable counterpart – nitrogen – 14. Consider the three atoms: [1] P-31; [2] F-19; & [3] H-2. For each atom give the following information: (a) the atomic number; (b) the total number of electrons in the neutral atom; ( c ) the number of valence electrons; and (d) the group number. List the various types of chemical bonds found in nature. Elucidate the differences between chemical bond types. Include in your response intermolecular forces expected in varying bond types.

Structure & Bonding is favorable because it leads to lowered energy and increased stability. Ionic compounds exist as a lattice with repeating cation/anion structure.

Structure & Bonding Isomers are different molecules having the same molecular formulae but different structural formulae. Example) C 2 H 6 O • Expected chemical & physical properties? • Observed intermolecular forces? • Which of the two would you expect to have a higher vapor pressure? • Which of the two would you expect to evaporate faster? • Which of the two would you expect higher volatility?

• Most common elements in organic compounds – C, O, N, and halogens – follow the octet rule. Hydrogen is an exception, of course, because it follows a “duet” as opposed to the “octet” due to its atomic structure. • What are some other exceptions? Incomplete or expanded octets such as Be. F 2 or SF 6? Why do these central atoms defer from the regularly accepted OCTET RULE…. ? • For organic chemists, phosphorous & Sulphur are common “rule breakers” because they are located in the third row of the periodic table. This means that they have unoccupied d orbitals which can accommodate for extra electrons…hence the expanded octet. Fosamax! Prevents osteoporosis….

Structure & Bonding RESONANCE!! Some molecules can’t be represented by a single Lewis Structure. What are the two possible resonance structures for the anion HCONH- ? Determine formal charge on the carbon atom as well as the nitrogen atom for each resonance structure. Remember…when you have a double bond to an oxygen (common), there will be resonance! Remember…when you have a charge, you have more or fewer electrons to work with! Remember…when you have any double bond (pi bond), your electrons are delocalized! What does delocalized electron configuration mean?

Structure & Bonding RULES FOR DRAWING RESONANCE STRUCTURES…. 1) How many TOTAL valence electrons are you working with? Are you working with an ion? (Remember bonding rules…e. g. hydrogen, beryllium, boron – incomplete octet & phosphorous, sulfur, etc – expanded octets) 2) Resonance structures differ in the position of multiple bonds and nonbonded electrons. The placement of atoms and single bonds always stays the same. Double bonds will switch positions. 3) Two resonance structures will have the same number of unpaired electrons. 4) Resonance structures must be valid Lewis structures. REMINDER - hydrogen must have two electrons & no second-row element can have more than eight electrons. CURVED ARROW NOTATION is a convention that shows how electron position differs between two resonance forms. This notation shows the movement of an electron pair OR a single electron. The tail of the arrow always begins at an electron pair (or a single electron). The head points to where the electron(s) “moves”.

Carbons carrying a + formal charge are call CARBOCATIONS.

Structure & Bonding Carbon atoms carrying a negative charge are called CARBANIONS. Often, carbon atoms carry a formal charge in an organic compound – however briefly. ? !? !? – intermediates… Hypothesize & Predict – are carbon atoms carrying a charge expected to be stable? Why or why not?

Structure & Bonding Resonance hybrid is a composite of all possible resonance structures. In resonance hybrids, electron pairs are drawn in different locations in individual resonance structures and are DELOCALIZED - this delocalization lends stability to the compound. Why? – because the negative charge of the non-static electron cloud is distributed over the compound and can “migrate” from atom to atom. Favorable resonance structures have MORE BONDS and FEWER CHARGES.

Structure & Bonding What is bond length? What is atomic radius and how does it trend? What is the relationship between bond length and atomic radius? What is bond energy? What is the relationship between bond length and bond energy?

POP QUIZ!!! Draw four 3 D representations for dichloromethane (wedges and dashes time).

Structure & Bonding DRAWING ORGANIC STRUCTURES. . . Two main types of shorthand representations for organic compounds – condensed structures & skeletal structures. Condensed structures are usually used for compounds having a chain of atoms bonded together, rather than a ring. CONVENTIONS… All atoms are drawn in, but the two-electron bond lines are omitted. Atoms are usually drawn next to the atoms to which they are bonded. Parentheses are used around similar groups bonded to the same atom. Lone pairs are omitted. To interpret condensed formulae, start at the left side of the molecule and remember that carbon atoms MUST BE TETRAVALENT…

Practice with condensed formulae…

Structure & Bonding DRAWING ORGANIC STRUCTURES… Two main types of shorthand representations for organic compounds – condensed structures & skeletal structures. Skeletal structures are used for organic compounds containing both rings and chains of atoms. CONVENTIONS… Assume there is a carbon atom at the junction (AKA verteces) of any two lines or at the end of any line. Assume there are enough hydrogen atoms around each carbon to make it tetravalent. Draw in all heteroatoms and the hydrogens directly bonded to them. (if any) A heteroatom, in organic chemical structures, is any atom that is not CARBON or HYDROGEN.

Practice with skeletal formulae…

Structure & Bonding

Structure & Bonding SKELETAL STRUCTURES WITH CHARGED CARBON ATOMS…((What? ! Carbon can be charged? ? Yup!! )) Conventions when interpreting skeletal structures for positively & negatively charged carbon atoms – hydrogen atoms and lone pairs are omitted SO: 1) A charge on a carbon atom takes the place of one hydrogen atom. 2) The charge determines the number of lone pairs. Negatively charged carbon atoms have one lone pair and positively charged carbon atoms have none. CARBOCATION! CARBANION!

A neutral O atom “owns” 6 electrons… two bonds (four bonding electrons) two lone pairs (four unshared electrons) How many carbons represented by this skeletal structure? Identify heteroatom(s) in this skeletal structure. Intermolecular forces expected from this substance? Most significant? Least significant?

Practice…

Independent Research… Hybridization. Orbital shapes. s, p, d, f…. Sigma bonds. Pi bonds. Delocalized electrons. Free rotation about a single covalent bond. Fixed positions about a multiple covalent bond.

Structure & Bonding ETHANE, ETHYLENE & ACETYLENE… Valid 2 -D Lewis Structure? Geometry about each central atom? 3 -D representation using wedges/dashes convention? Sigma bonds and/or pi bonds? Hybridization about carbon atoms? Hydrogen atoms? Fixed or free rotation about the C-C bond?

Structure & Bonding ETHANE, ETHYLENE & ACETYLENE… Valid 2 -D Lewis Structure? Geometry about each central atom? 3 -D representation using wedges/dashes convention? Sigma bonds and/or pi bonds? Hybridization about carbon atoms? Hydrogen atoms? Fixed or free rotation about the C -C bond?

Structure & Bonding Bond Length vs Bond Strength As the number of electrons between two nuclei INCREASES, bonds become shorter and stronger. Triple bonds are shorter and stronger than double bonds. Double bonds are shorter and stronger than single bonds. So this is what type of relationship?

Structure & Bonding Electronegativity & Bond Polarity How does EN trend across and down the periodic table? What about noble gases?

Structure & Bonding Determining polarity of molecules: Use EN differences to identify all polar bonds and directions of bond dipoles. Determine geometry around individual atoms by considering groups. Decide if individual dipoles cancel or reinforce each other in space.

Structure & Bonding

Structure & Bonding Levo-Dopa is a representative organic molecule and applicable to mammalian biochemistry. It is used to treat Parkinson’s disease. All organic molecules, regardless of size or complexity, behave similarly depending on polarity, IMF’s & geometry.

Structure & Bonding Determine the hybridization and geometry around every atom. Label all polar and nonpolar bonds. Compare bond length and bond strength for bonds. These fundamental properties about a molecule determine physical property and chemical property behavior.

TEST PRACTICE with Levo-Dopa…