Organic Chemistry Second Edition Chapter 1 David Klein

Organic Chemistry Second Edition Chapter 1 David Klein
A Review of General Chemistry: Electrons, Bonds, and Molecular Properties Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

1.1 Organic Chemistry The study of carbon-containing molecules and their reactions What happens to a molecule during a reaction? A collision Bonds break/form The BIG question: WHY do reactions occur? We will need at least 2 semesters of your time to answer this question FOCUS ON THE ELECTRONS Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

1.1 Organic Chemistry Wöhler, 1928 Klein, Organic Chemistry 2e
Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

1.2 Structural Theory Klein, Organic Chemistry 2e

1.2 Structural Theory Atoms that are most commonly bonded to carbon include N, O, H, and halides (F, Cl, Br, I). With some exceptions, each element generally forms a specific number of bonds with other atoms Practice with SkillBuilder 1.1 Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

1.3 Covalent Bonding How do potential energy and stability relate?
What forces keep the bond at the optimal length? Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

1.3 Atomic Structure A review from General Chemistry
Protons (+1) and neutrons (neutral) reside in the nucleus Electrons (-1) reside outside the nucleus. Some electrons are close to the nucleus and others are far away. Look at carbon for example. Which electrons are the valence electrons? Why are valence electrons important? Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

1.3 Counting Valence Electrons
You can always calculate the number of valence electron by analyzing the e- configuration. Or, for Group A elements only, just look at the Group number (Roman Numeral) on the periodic table Practice with SkillBuilder 1.2 Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

1.3 Simple Lewis Structures
For simple Lewis Structures… Draw the individual atoms using dots to represent the valence electrons. Put the atoms together so they share PAIRS of electrons to make complete octets. WHAT is an octet? Take NH3, for example… Practice with SkillBuilder 1.3 Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

1.3 Simple Lewis Structures
For simple Lewis Structures… Draw the individual atoms using dots to represent the valence electrons. Put the atoms together so they share PAIRS of electrons to make complete octets. WHAT is an octet? Try drawing the structure for C2H2 Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

1.4 Formal Charge What term do we use to describe atoms with an unbalanced or FORMAL charge? How does formal charge affect the stability of an atom? Atoms in molecules (sharing electrons) can also have unbalanced charge, which must be analyzed, because it affects stability To calculate FORMAL charge for an atom, compare the number of valence electrons that should be associated with the atom to the number of valence electrons that are actually associated with an atom Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

1.4 Formal Charge Consider the formal charge example below. Calculate the formal charge on each atom. or Carbon should have 4 valence electrons, because it is in group IVA on the periodic table. Carbon actually has 8 valence electrons. It needs 8 for its octet, but only 4 count towards its charge. WHY? The 4 it actually has balance out the 4 it should have, so it does not have formal charge. Its neutral. Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

1.4 Formal Charge Analyze the formal charge of the oxygen atom. or
Oxygen should have 6 valence electrons, because it is in group VIA on the periodic table. It actually has 8 valence electrons. It needs 8 for its octet, but only 7 count towards its charge. WHY? If it actually has 7, but it should only have 6, what is its formal charge? Practice with SkillBuilder 1.4 Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

1.5 Polar Covalent Bonds Covalent bonds are electrons pairs that exist in an orbital shared between two atoms. What do you think that orbital looks like? Just like an atomic orbital, the electrons could be anywhere within that orbital region. What factors determine which atom in the bond will attract the shared electrons more? Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

1.5 Polar Covalent Bonds Covalent bonds are either polar or nonpolar
Nonpolar Covalent –bonded atoms share electrons evenly Polar Covalent – One of the atoms attracts electrons more than the other Electronegativity - how strongly an atom attracts shared electrons Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

1.5 Polar Covalent Bonds Electrons tend to shift away from lower electronegativity atoms to higher electronegativity atoms. The greater the difference in electronegativity, the more polar the bond. Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

1.6 Atomic Orbitals General Chemistry review
In the 1920s, Quantum Mechanics was established as a theory to explain the wave properties of electrons The solution to wave equations for electrons provides us with visual pictures called orbitals Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

1.6 Atomic Orbitals General Chemistry review
The type or orbital be identified by its shape An orbital is a region where there is a calculated 90% probability of finding an electron. The remaining 10% probability tapers off as you move away from the nucleus Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

1.6 Atomic Orbitals Electrons behave as both particles and waves. How can they be BOTH? Maybe the theory is not yet complete The theory does match experimental data, and it has predictive capability. Like a wave on a lake, an electron’s wavefunction can be (+), (–), or ZERO. Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

1.6 Atomic Orbitals Because they are generated mathematically from wavefunctions, orbital regions can also be (–), (+), or ZERO The sign of the wave function has nothing to do with electrical charge. In this p-orbital, there is a nodal plane. The sign of the wavefunction will be important when we look at orbital overlapping in bonds. Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

1.6 Atomic Orbitals Electrons are most stable (lowest in energy) if they are in the 1s orbital? The 1s orbital is full once there are two electrons in it. Why can’t it fit more? The 2s orbital is filled next. The 2s orbital has a node. WHERE? Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

1.6 Atomic Orbitals Once the 2s is full, electrons fill into the three degenerate 2p orbitals Where are the nodes in each of the 2p orbitals? Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

1.6 Atomic Orbitals Common elements and their electron configurations
Practice with SkillBuilder 1.6 Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

1.7 Valence Bond Theory A bond occurs when atomic orbitals overlap. Overlapping orbitals is like overlapping waves Only constructive interference results in a bond Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

1.7 Valence Bond Theory The bond for a H2 molecule results from constructive interference Where do the bonded electrons spend most of their time? Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

1.8 Molecular Orbital Theory
Atomic orbital wavefunctions overlap to form MOs that extend over the entire molecule. MOs are a more complete analysis of bonds, because they include both constructive and destructive interference. The number of MOs created must be equal to the number of AOs that were used. H2 MOs Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

Why is the antibonding orbital higher in energy? When the AOs overlap, why do the electrons go into the bonding MO rather than the antibonding MO? Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

Imagine a He2 molecule. How would its MOs compare to those for H2? In general, if a molecule has all of its bonding and antibonding MOs occupied, will it be stable or unstable? How would the energy of the He2 compare to 2 He? Why does Helium exist in its atomic form rather than in molecular form? Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

Consider TWO of the many MOs that exist for CH3Br There are many areas of atomic orbital overlap Notice how the MOs extend over the entire molecule Each picture below represents ONE orbital. Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

How many electrons can fit into the areas represented? In the ground state, electrons occupy some MOs and not others, WHY? Depending on the circumstances, we will use both MO and valence bond theory to explain phenomena Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

1.9 Hybridized Atomic Orbitals
Given the electron configuration for C and H, imagine how their atomic orbitals might overlap Would such orbital overlap yield methane? Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

To make methane, the C atom must have 4 atomic orbitals available for overlapping If an electron is excited from the 2s to the 2p, will that make it suitable for making methane? If four H atoms were to come in and overlap with the 2s and 2p orbitals, what geometry would the resulting methane have? Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

The carbon must undergo hybridization to form 4 equal atomic orbitals The atomic orbitals must be equal in energy to form four equal-energy symmetrical C-H bonds Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

Draw a picture that shows the necessary atomic orbitals and their overlap to form ethane (C2H6). Draw a picture that shows the necessary atomic orbitals and their overlap to form water. Practice with conceptual checkpoint 1.19 Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

Consider ethene (ethylene). Each carbon in ethene must bond to three other atoms, so only three hybridized atomic orbitals are needed Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

An sp2 hybridized carbon will have three equal-energy sp2 orbitals and one unhybridized p orbital Which is lower in energy, the sp2 or the p? Why? Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

The unhybridized p orbitals in ethene form pi (π) bonds, SIDE-BY-SIDE overlap Practice with conceptual checkpoint 1.20 Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

The unhybridized p orbitals in ethene form pi (π) bonds, SIDE-BY-SIDE overlap of p-orbitals giving both CONSTRUCTIVE and DESTRUCTIVE interference MO theory shows the orbitals that result. Remember, red and blue regions are all part of the same orbital Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

Consider ethyne (acetylene). Each carbon in ethyne must bond to two other atoms, so only two hybridized atomic orbitals are needed Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

The sp atomic orbitals overlap HEAD-ON to form sigma (σ) bonds while the unhybridized p orbitals overlap SIDE-BY-SIDE to form pi bonds Practice with SkillBuilder 1.7 Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

Which should be stronger, a pi bond or a sigma bond? WHY? Which should be longer, an sp3 – sp3 sigma bond overlap or an sp – sp sigma bond overlap? Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

1.10 Molecular Geometry Valence shell electron pair repulsion (VSEPR theory) Valence electrons (bonded and lone pairs) repel each other To determine molecular geometry… Determine the Steric number Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

1.10 Molecular Geometry Valence shell electron pair repulsion (VSEPR theory) Valence electrons (bonded and lone pairs) repel each other To determine molecular geometry… Predict the hybridization of the central atom If the Steric number is 4, then it is sp3 If the Steric number is 3, then it is sp2 If the Steric number is 2, then it is sp Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

1.10 sp3 Geometry For any sp3 hybridized atom, the 4 valence electron pairs will form a tetrahedral electron group geometry Methane has 4 equal bonds, so the bond angles are equal How does the lone pair of ammonia affect its geometry? The bond angels in oxygen are even smaller, why? Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

1.10 sp2 Geometry Calculate the Steric number for BF3
Electron pairs that are located in sp2 hybridized orbitals will form a trigonal planar electron group geometry What will be the molecular geometry? Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

1.10 sp2 Geometry How many electrons are in Boron’s unhybridized p orbital? Does this geometry follow VSEPR theory? Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

1.10 sp2 Geometry Analyze the steric number, hybridization, electron group geometry and molecular geometry for this imine? Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

1.10 sp Geometry Analyze the Steric number, the hybridization, the electron group geometry, and the molecular geometry for the following molecules BeH2 CO2 Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

1.10 Geometry Summary Practice with SkillBuilder 1.8

1.11 Molecular Polarity Electronegativity Differences cause induction
Induction (shifting of electrons WITHIN their orbitals) results in a dipole moment. Dipole moment = (the amount of partial charge) x (the distance the δ+ and δ- are separated) Dipole moments are reported in units of debye (D) 1 debye = esu ∙ cm An esu is a unit of charge. 1 e- has a charge of 4.80 x esu cm are included in the unit, because the distance between the centers of + and – charges affects the dipole Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

1.11 Molecular Polarity Consider the dipole for CH3Cl
Dipole moment (μ) = charge (e) x distance (d) Plug in the charge and distance μ = (1.056 x esu) x (1.772 x 10-8 cm) Note that the amount of charge separation is less than what it would be if it were a full charge separation (4.80 x esu) μ = 1.87 x esu ∙ cm Convert to debye μ = 1.87 D Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

1.11 Molecular Polarity What would the dipole moment be if CH3Cl were 100% ionic? μ = charge (e) x distance (d) Plug in the charge and distance μ = (4.80 x esu) x (1.772 x 10-8 cm) The full charge of an electron is plugged in μ = 8.51 x esu ∙ cm = 8.51 D What % of the C-Cl bond is ionic? Is the C-Cl bond mostly ionic or mostly covalent? Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

1.11 Molecular Polarity For molecules with multiple polar bonds, the dipole moment is the vector sum of all of the individual bond dipoles Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

1.11 Molecular Polarity It is important to determine a molecule’s geometry FIRST before analyzing its polarity If you have not drawn the molecule with the proper geometry, it may cause you to assess the polarity wrong as well Would the dipole for water be different if it were linear rather than angular? Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

1.11 Molecular Polarity Practice with SkillBuilder 1.9

1.12 Intermolecular Forces
Many properties such as solubility, boiling point, density, state of matter, melting point, etc. are affected by the attractions BETWEEN molecules Neutral molecules (polar and nonpolar) are attracted to one another through… Dipole-dipole interactions Hydrogen bonding Dispersion forces (a.k.a. London forces or fleeting dipole-dipole forces) Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

1.12 Dipole-Dipole Dipole-dipole forces result when polar molecules line up their opposite charges. Note acetone’s permanent dipole results from the difference in electronegativity between C and O The dipole-dipole attractions BETWEEN acetone molecules affects acetone’s boiling and melting points. HOW? Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

1.12 Hydrogen Bonding Hydrogen bonds are an especially strong type of dipole-dipole attraction Hydrogen bonds are strong because the partial + and – charges are relatively large Why are the partial charges in the H-bonding examples below relatively large? Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

1.12 Hydrogen Bonding Only when a hydrogen shares electrons with a highly electronegative atom (O, N, F) will it carry a large partial positive charge The large δ+ on the H atom can attract large δ– charges on other molecules Even with the large partial charges, H-bonds are still about 20 times weaker than covalent bonds Compounds with H atoms that are capable of forming H-bonds are called protic Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

1.12 Hydrogen Bonding Which of the following solvents are protic (capable of H-bonding), and which are not? Acetic acid Diethyl ether Methylene chloride (CH2Cl2) Dimethyl sulfoxide Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

1.12 Hydrogen Bonding H-bonds are among the forces that cause DNA to form a double helix and some proteins to fold into an alpha-helix Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

1.12 London Dispersion Forces
If two molecules are nonpolar (dipole = 0 D), will they attract one another? YES! HOW? Nonpolar molecules normally have their electrons (–) spread out evenly around the nuclei (+) completely balancing the charge However, the electrons are in constant random motion within their MOs Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

The constant random motion of the electrons in the molecule will sometimes produce an electron distribution that is NOT evenly balanced with the positive charge of the nuclei Such uneven distribution produces a temporary dipole, which can induce a temporary dipole in a neighboring molecule Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

The result is a fleeting attraction between the two molecules Such fleeting attractions are generally weak. But like any weak attraction, if there are enough of them, they can add up to a lot Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

The greater the surface area of a molecule, the more temporary dipole attractions are possible Consider the feet of Gecko. They have many flexible hairs on their feet that maximize surface contact The resulting London dispersion forces are strong enough to support the weight of the Gecko Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

1.13 Solubility We use the principle, like-dissolves-like
Polar compounds generally mix well with other polar compounds If the compounds mixing are all capable of H-bonding and/or strong dipole-dipole, then there is no reason why they shouldn’t mix Nonpolar compounds generally mix well with other nonpolar compounds If none of the compounds are capable of forming strong attractions, then no strong attractions would have to be broken to allow them to mix Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

1.13 Solubility We know it is difficult to get a polar compound (like water) to mix with a nonpolar compound (like oil) We can’t use just water to wash oil off our dirty cloths To remove nonpolar oils, grease, and dirt, we need soap Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

1.13 Solubility Soap molecules organize into micelles in water, which form a nonpolar interior to carry away dirt. Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

1.13 Solubility Which attraction is generally stronger?
The attraction between a permanent dipole and an induced dipole versus The attraction between a temporary dipole and an induced dipole The attraction between a polar molecule and a nonpolar molecule The attraction between two nonpolar molecules? Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

1.13 Solubility Why won’t a nonpolar compound readily dissolve in water? Is it because the water molecules repel the nonpolar molecules? Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

Additional Example Problems
Draw the structure for C2Cl3N Draw the structure for CH2O Draw the structure for CH2O2 Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

How many nodes are in the 3s subshell? How many nodes are in a typical sigma antibonding MO? How many nodes are in a typical sp3 orbital? How many nodes are in a typical pi bonding MO? How many nodes are in a typical pi antibonding MO Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

Organic Chemistry Second Edition Chapter 1 David Klein

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