ORGANIC - BROWN 8E CH.1 - COVALENT BONDING AND SHAPES OF MOLECULES

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CONCEPT: WHAT IS ORGANIC CHEMISTRY? Organic Chemistry is the chemistry of life. It consists of the study of molecules that are (typically) created and used by biological systems.

2 CONCEPT: WHAT IS ORGANIC CHEMISTRY? Organic Chemistry is the chemistry of life. It consists of the study of molecules that are (typically) created and used by biological systems. Burt s Bees Very Volumizing Shampoo ($18) Creating Nerve Gases Technically, an organic molecule is any molecule that contains both and. An organic molecule that contains a mixture of carbon and hydrogen solely is called a EXAMPLE: Which molecules are organic? Which of them are also hydrocarbons? Page 2

3 CONCEPT: ATOMIC STRUCTURE The atom is the basic unit of matter. The atomic number of an atom is equal to the number of The mass number of an atom is equal to + Isotopes have the same atomic number but have differing EXAMPLE: Hydrogen Isotopes Electrons orbit the nucleus in a region of space that is called a The region of space within a shell with exactly enough space for a pair of electrons (up/down spin) is called an When atoms possess a different number of electrons than protons, they are called Positively charged atoms are called Negatively charged atoms are called EXAMPLE: Hydrogen Ions Three Principles of Electron Configuration Page 3

4 PRACTICE: Determine the number of protons, neutrons and electrons in the following atoms. a. b. PRACTICE: Determine which of the three principles of electron configuration is being broken in the electron diagrams below. c. d. Page 4

5 CONCEPT: WAVE FUNCTIONS Quantum Mechanics states that electrons behave both as particles and as. The Heisenberg Uncertainty Principle states that we cannot simultaneously know an electron s speed and Equations called wave functions correspond to the energy state of a given electron The relative probability of finding an electron can be derived from the wave function The 3-D plot of the is called an atomic : where the chance of finding electrons is high. As with any type of wave, wave functions have the ability to with each other upon meeting. This can occur either constructively or destructively EXAMPLE: H2 Molecular Orbitals Page 5

6 CONCEPT: MOLECULAR ORBITALS When atomic orbitals overlap constructively, they create unusual regions of shared electron density called The type of bond created is determined by how many regions are overlapping We can use a model called the Linear Combination of Atomic Orbitals (LCAO) using addition and subtraction of orbitals to indicate the type of interference. This way we can determine the mathematical energy levels of all possible molecular orbitals. EXAMPLE: H2 LCAO EXAMPLE: C2 LCAO (simplified) Page 6

7 CONCEPT: BOND SUMMARY EXAMPLE: Determine the number of σ-bonds and π-bonds in the following molecules a. b. PRACTICE: Rank the following bonds from shortest to longest Page 7

8 CONCEPT: THE OCTET RULE Atoms are most stable when they achieve the number of electrons necessary to reach a Noble Gas Configuration. The tendency for atoms to lose or gain electrons in order to reach this configuration is known as the rule We can use MO theory to prove why atoms are most stable (and will not form bonds) in the Noble gas configuration EXAMPLE: He2 LCAO Atoms can satisfy their octet through forming chemical bonds or by possessing lone pairs. These are called octet electrons. First-row elements (H, He, Li) will prefer to possess octet electrons Second-row elements (C, N, O, F) will prefer to possess octet electrons Atoms smaller than Carbon will possess less than 8 electrons: (Be) and (B) Third-row elements may form expanded octets that can hold (P) and (S) Page 8

9 CONCEPT: BONDING PREFERENCES There may be many ways to combine octet electrons to satisfy the octet rule for a certain atom: electrons are the name we give to the octet electrons that the atom actually owns. The number of these determines which of the possible octets will be the most stable. An atom owns every lone electron it has An atom owns electron for every bond that it has EXAMPLE: Find the total number of octet electrons and valence electrons in the following hydrocarbons. Do all of these compounds satisfy the octet rule? If so, are they all equally stable? The amount of electrons that the valence shell of each 2 nd row element prefers to own is determined by its group number on the periodic table. This will determine how many bonds it wants to have in its most stable state. Page 9

10 CONCEPT: FORMAL CHARGES Whenever there is a difference between the number of valence electrons that an atom has and its group number, a formal charge is assigned. FORMAL CHARGE = Group # - Valence Electrons The is the term that we give to the SUM of all the formal charges of a molecule. EXAMPLE: Calculate the formal charges of ALL atoms. PRACTICE: Calculate the formal charges of ALL atoms. Indicate if the molecule has a net charge. a. b. Page 10

11 CONCEPT: BONDLINE STRUCTURES The bondline method is a way to simplify the drawings of organic structures, based on the octet rule. are implied: Every corner is assumed to represent a carbon. are implied: Carbon is assumed to possess enough hydrogens to fill its octets. are implied: Heteroatoms are assumed to possess enough electrons to fill their octets. are used to indicate when an atom does not satisfy its bonding preference. Watch Out: ALL hydrogens on MUST be drawn explicitly. EXAMPLE: Conversion of ethanol to bondline PRACTICE: How many implied hydrogens does each labeled carbon have? a. b. Page 11

12 PRACTICE: Convert each structure into a line-angle structure. Be sure to assign ALL necessary formal and net charges. a. b. c. d. Page 12

13 CONCEPT: LEWIS STRUCTURES Lewis structures are used to determine chemical structures based on based on the octet rule and bonding preferences. 1. Draw the atom with highest bond preference in the middle and propose a σ-bond framework. a. If two atoms have the same bonding preference, place the bigger one in the center 2. Complete octets using lone pairs 3. Calculate the theoretical number of valence electrons 4. Calculate the actual number of valence electrons 5. Actual Theoretical = Electron Difference a. If electron difference is positive, create double bonds b. If electron difference is negative, add lone pairs. EXAMPLE: N2H4 Lewis Structure PRACTICE: Draw the Lewis Structure for the following molecules: HCN Page 13

14 PRACTICE: Draw the Lewis Structures for the following molecules a. HNO3 b. H2CO3 Page 14

15 CONCEPT: CONDENSED STRUCTURES The condensed method is a common way to describe the of a molecule using only text. Know how to quickly interconvert between and condensed EXAMPLE: Full Condensed Structure EXAMPLE: Condensed Mixed Structure PRACTICE: Convert the following condensed structures into bondline CH2Br(CH2)3CH(CH2CH3)2 Page 15

16 CONCEPT: RESONANCE STRUCTURES Resonance theory is used to represent all the different ways that the same molecule can distribute its electrons. Atoms move! The only thing that moves is of these contributing structures will be a realistic representation of what the molecule actually looks like Rules: Use curved arrows to represent electron movement Use double-sided arrows and to link related structures to each other Arrows always travel from region of electron density to electron density The net charge of each structure must be EXAMPLE: Common forms of resonance Page 16

17 PRACTICE: Draw all of the contributing structures for the following molecules a. b. c. Page 17

CONCEPT: RESONANCE HYBRIDS The resonance hybrid represents the mathematical combination of all the contributing structures It indicates where the resonating electrons within the molecule are to

18 CONCEPT: RESONANCE HYBRIDS The resonance hybrid represents the mathematical combination of all the contributing structures It indicates where the resonating electrons within the molecule are to reside EXAMPLE: Isocyanate Resonance Hybrid CONCEPT: MAJOR CONTRIBUTORS Often one of the resonance structures will be more so it will contribute to the more than the others. Major contributors will often have the following characteristics: structures are almost always more stable than charged ones If possible, every atom should fill its Use electronegativity trends to determine best placement of charges EXAMPLE: Isocyanate major contributor Page 18

19 PRACTICE: Draw all of the contributing structures for the following molecules. Label the major contributor if applicable and draw the resonance hybrid. a. b. Page 19

20 CONCEPT: MOLECULAR GEOMETRY Molecular geometry is based on VSEPR theory: Bond sites will each other as much as possible. The molecular geometry predicts what shape the hybridized atom will have. EXAMPLE: Predict the hybridization and molecular geometry of the following selected atoms: Page 20

21 PRACTICE: Determine the hybridization and molecular geometry of the following selected atoms: a. b. Page 21

22 CONCEPT: HYBRID ORBITAL THEORY The Aufbau Principle states that electrons fill orbitals in order of increasing energy. If carbon has only two unfilled orbitals, why does it like to make 4 bonds? EXAMPLE: Carbon sp 3 Hybridization Many atoms prefer to blend some of their 2 nd shell orbitals together to make new orbitals Page 22

23 CONCEPT: HYBRIDIZATION SUMMARY Hybridization can be predicted by the determine the number of on an atom Where a bond site is equal to any or EXAMPLE: Predict the hybridization of the following reactive intermediates Page 23

24 CONCEPT: ELECTRONEGATIVITY Chemical bonds are formed when the sharing of valance electrons between two or more atoms takes place. The of sharing will determine the identity and strength of the chemical bond. An unequal sharing of electrons in one direction along a bond is called a ( ) The charge between any two bonded atoms is related to their difference in electronegativity Generalizations: Bonds to carbon and hydrogen are always Bonds between two identical atoms are always Adjacent atoms on the periodic table are Lone pairs are exist when atoms have asymmetrical dipoles Page 24

25 PRACTICE: Which of the following molecules contain dipoles? Which contain net dipoles? PRACTICE: Which of the solvents below is apolar? Which is polar? Page 25

26 CONCEPT: FUNCTIONAL GROUPS We can group several millions of different molecules into subsets of similar 1. Hydrocarbons All carbon groups regardless of size can be symbolized using an group. When an alkane is attached to a greater carbon chain, it is given an suffix. (i.e. group) Carbons are given a degree based on how many other they are attached to Hydrogens possess the degree as the carbon they are attached to Degrees are expressed as primary, secondary, tertiary and quaternary (1⁰, 2⁰, 3⁰, 4⁰) EXAMPLE: Determine the degree of the indicated carbons and hydrogens Page 26

27 2. Alkyl Halide Any R group directly attached to a halogen. The degree of alkyl halide is determined the same way as The carbonyl is NOT a functional group, but it is a major component of many functional groups 3. Alcohol 6. Carboxylic Acid ( ) Degree of alcohol is determined the same The acid of organic chemistry way as 4. Amine 7. Amide ( ) Degree of alcohol is determined the same Degree of alcohol is determined the same way as. way as. 5. Ether 8. Ester ( ) Page 27

28 9. Carbonyls The term carbonyl is not the proper name of the functional groups because the functionality of the group depends on its location on the carbon chain.. Ketone ( ) Aldehyde ( ) - carbonyl group - carbonyl group 10. Nitrile 11. Benzene Directly attached to R group ( )( ) Extra CH2 between R group ( )( ) EXAMPLE: Identify all the functional groups in the following compound. Show degrees where applicable. Page 28

29 12. Other Carbonyl Compounds Acyl Chloride ( ) Anhydride ( ) 13. Sulfur Compounds Page 29

30 PRACTICE: Identify all the functional groups in the following compound. Show degrees where applicable. a. b. c. Page 30

ORGANIC - CLUTCH CH. 1 - A REVIEW OF GENERAL CHEMISTRY.

ORGANIC - CLUTCH CH. 1 - A REVIEW OF GENERAL CHEMISTRY. !! www.clutchprep.com CONCEPT: WHAT IS ORGANIC CHEMISTRY? Organic Chemistry is the chemistry of life. It consists of the study of molecules that are (typically) created and used by biological systems.