ORGANIC - KLEIN 3E CH.1 - A REVIEW OF GENERAL...

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ORGANIC - KLEIN 3E

CH.1 - A REVIEW OF GENERAL CHEMISTRY

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.

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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?

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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

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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.

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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

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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)

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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

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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) _______

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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 2nd 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.

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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.

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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.

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

a.

b.

c.

d.

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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

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

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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

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CONCEPT: INDEX OF HYDROGEN DEFICIENCY (STRUCTURAL)

A saturated molecule is any molecule that has the maximum number of hydrogens possible for its chemical structure. The

rule that we use for this is _____________.

● Any molecule that has less than __________ number of hydrogens is considered to be __________________.

EXAMPLE: How many hydrogens must the following carbon skeletons contain to be saturated? Are they missing any?

IHD rules give us the ability to quickly determine which molecules are more saturated and which molecules are less

saturated with hydrogen.

● 1 IHD = Compound is missing ___ hydrogens.

□ Rings/Double bonds = _____

□ Triple Bonds = ______

EXAMPLE: What is the degree of unsaturation of the following compounds?

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CONCEPT: INDEX OF HYDROGEN DEFICIENCY (MOLECULAR FORMULA)

□ Molecular Formula:

- When given only the molecular formula of the molecule use the following rules.

(Theoretical # H’s – Actual # H’s) / 2 = IHD, where: ● H / X = _______ ● O = ______ ● N = ______

EXAMPLE: What is the IHD for each of the following compounds?

a. C4H7Cl

b. C6H7N

c. C7H12O2

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CONCEPT: CONSTITUTIONAL ISOMERS

Constitutional isomers are molecules that have identical molecular formulas (all the same atoms), but have

different _______________________. You will be asked to compare molecules and determine how they are related.

EXAMPLE: How are the following two compounds related?

A) Identical Compounds

B) Constitutional Isomers

C) Different Compounds

Steps to solve Constitutional Isomer Problems:

Step 1. (Are the atoms all the same?) Count non-_______________ atoms and IHD in both compounds

- If not exactly the same, they are ____________________________

- If the same, then go to step 2

Step 2. (Are the atoms all connected the same?) Look for a _____________ atom, then count bonds from there.

-If not exactly the same, they are _______________________________

-If the same, then they are _____________________________

EXAMPLE: How are the following sets of compounds related?

A) Identical Compounds A) Identical Compounds

B) Constitutional Isomers B) Constitutional Isomers

C) Different Compounds C) Different Compounds

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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

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PRACTICE: Draw all of the contributing structures for the following molecules

a.

b. c.

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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

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

a.

b.

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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 sp3 Hybridization

● Many atoms prefer to blend some of their 2nd shell orbitals together to make new _________________________ orbitals

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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

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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:

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PRACTICE: Determine the hybridization and molecular geometry of the following selected atoms:

a.

b.

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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

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PRACTICE: Which of the following molecules contain dipoles? Which contain net dipoles?

PRACTICE: Which of the solvents below is apolar? Which is polar?

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ORGANIC - KLEIN 3E CH.1 - A REVIEW OF GENERAL...

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