Links to download Zoom Lecture Videos and PDF files
- Lecture Date: Tuesday, January 25, 2022
Welcome to Chem 12A. This was the first lecture of the spring semester for Chem 12A. In this lecture I introduce myself and the course. We looked at the syllabus and the ChemEd.Study website. We talked about what makes this course diffrent from the other chemistry courses. We then jumped into chapter 1 with a look at Lewis structures and common bonding patterns.
- Lecture Date: Thursday, January 27, 2022
In this lecture we look at common bonding patterns that result in formal charges. We show how the common bonding patterns can be used to quickly form Lewis structures for organic molecules. We examine the origin of the formal charge formula and show a quicker way of establishing formal charge that can be done without writing out a mathematical formula. We then moved to electronegativity and defining non-polar, polar and ionic bonds. We ended with a look at dipole moments for molecules and little look at molecular modeling as a tool for visualizing dipole moments.
- Lecture Date: Tuesday, February 1, 2022
This is where we really get started with a deep look at bonding. We begin with a look at why bonding takes place, how covalent bonds are formed and a qualitative look at the molecular orbital theory of bond formation. We actually take a look at two different model theories - Molecular Orbital Theory and Natural Bonding Theory. Most of the time we will work within Natural Bonding Theory, choosing to take a localized approach to hybridization and bond formation, but we will head into Molecular Orbital Theory when we deal with aromaticity, cycloadditions, spectroscopy and other appropriate topics. Lot's to digest in this lecture.
- Lecture Date: Thursday, February 3, 2022
We carry Tuesday's theme into today's lecture by continuing our look at natural bonding theory and hybridization. We extend the hybridization model of Sp3 for tetrahedral geometries to Sp2 for trigonal planar and Sp for linear. We look in depth at what those bonding schemes look like, including the π-bond (pi-bond). We also related relative bond length to hybridization. This is an extremely important concept. In fact we will link many important physical and chemical properties to hybridization. We ended with a couple of extremely important examples.
- Lecture Date: Tuesday, February 8, 2022
In today's lecture I pick up a few topics from chapter one that we didn't previously hit. We take a look at intermolecular attractive forces (IMF) and their influence on the physical properties of melting point and boiling point of compounds. With that we move into Chapter 2 dealing with Molecular Representations.Today we start with bond line formulas. So far we have been communicating with structural formulas or condensed molecular formulas, but these are both very slow. We need something faster. Bond line formulas reduce the Lewis structures to line structures only showing hetero atoms explicitly. Hydrogens are only shown when connected to a hetero atom or for the aldehyde proton. Proficiency in bond line formulas is critical following the lectures moving forward.
- Lecture Date: Thursday, February 10, 2022
It is resonance day. Today we start our look at resonance. The topic of resonance is extremely important, and yet the word resonance makes it sound as if it is no big deal, as compared to something like Molecular Orbital Theory. Just tagging the word "Theory" onto something makes it known that this is a tool for understanding something. Resonance should include "Theory" after it, as that is what it is, a theory or tool for understanding all kinds of molecular properties including stability, reactivity, electrophilicity, nucleophilicity, acidity and basicity, and a whole lot more. In fact, resonance is one of the most common answers to problems in organic chemistry. Careful though, while resonance is one of the most common answers, the answer is never just "resonance", but you must show all the resonance and interpret it properly. So let's get started.
- Lecture Date: Tuesday, February 15, 2022
Second day on resonance. In this lecture we hit a couple more examples of resonance problems. Here we look at a couple of very important ideas. The first is that not all resonance structures are important to look at. We want to look at the structures that delocalize charge and ignor structures that move double bonds but don't move the charge. The other idea is that we never want to take electrons away from oxygen. Oxygen may have a positive charge, but it must always maintain 8 valence electrons.
- Lecture Date: Thursday, February 17, 2022
We start chapter 3 and acid-base today. This is the first chapter where we have a "lot" of info that needs to be used together, sort of a union of many concepts. This is very common in organic chemistry to have a union of many concepts that are required to arrive at the correct answer to the problem at hand. The concepts include electronegativity, hybridization, resonance, size of the atom, and induction. On top of that we also have to recall acid-base concepts and put it all together with lewis bond structures. In many ways this chapter exemplifies the complexity that is organic chemistry, keeping in mind that we use all the information going forward even as we add new information to the top of the pile. So here we go with acid-base.
- Lecture Date: Tuesday, February 22, 2022
Today we do a deeper dive into acid-base. In today's lecture we complete the hierarchy of factors that control relative stability of both cations and anions. The factors are Electronegativity/hybridization, Resonance, Size, and Induction - in that order. We present pKa data to show this order is correct. We then use the ranking to address acid-base problems. The main problem types are find the most acidic proton in a molecule, the most basic position in a molecule, rank the molecules from least acidic to most, or least basic to most, and finally explain the given pKa's. We well cover all the problem types in lecture - many of them will serve to highlight things to watch for. We will cover about half of these problem types in this lecture and the other half on Thursday.
- Lecture Date: Thursday, February 24, 2022
This lecture covers the last day on Chapter 3 Acid and Base, and starts Chapter 4 Alkanes. The majority of the lecture is Acid and Base, with only the last few minutes introducing Alkanes. This lecture really brings a lot of what we have been discussing into sharp focus. We looked at an additional example of relative basicity. So much of what we have been doing is acidity, it was good to have another basicity example. We then focused on the other core skill here, which is how to groups affect acidity or basicity. This is a critical skill as well. Groups can have very different affects depending on what they are attached to, what position they are attached to, and how they are attached. Some groups are one trick ponies, others can have two or three different effects depending on the factors. This lecture nails all that down for you.
- Lecture Date: Tuesday, March 1, 2022
As we launch into Chapter 4 on alkanes, this lecture starts us off taking a closer look at constitutional and geometric isomers. Here we introduce frameworks, a way of using the carbon backbone to organize a systematic approach to drawing all isomers without missing or duplicating structures. Several examples are shown. Next up we start our look at nomenclature. We got through the basics of the organic nomenclature system. A couple of examples were presented, however we will present more examples in the next lecture on Thursday.
- Lecture Date: Thursday, March 3, 2022
We continue our discussion of nomenclature with a deeper look at the complex side chain nomenclature and several more examples of naming compounds. Once we completed nomenclature we turn our attention to conformations of alkanes. We show how to draw Newman projections and how to use them to analyse different conformations to find the lowest energy conformation.
- Lecture Date: Tuesday, March 8, 2022
Progressing in chapter 4 today we started by looking a little more at Newman projections and determining the lowest energy conformation for a molecule with more than two substituents. From there we moved into cyclic alkanes and examined their bonding structure and conformations. We show how to draw conformations of 5-member rings in newman projections, and how to use two Newmans together to draw conformations of 6-member ring systems. We also showed how to draw these systems in chair and boat conformations and examined the energy of conformations relating to a substituent in the axial position as relative to the equatorial position.
- Lecture Date: Thursday, March 10, 2022
Today we further explored the conformations of six-member rings. We looked at the different sizes of substituents and their impact on the percentage of molecules that will exist with that substituent in the equatorial position. We also examined how to analyse the lowest energy conformation of a molecule with multiple substituents. Next up we looked at joined ring systems, spiro and bicyclo compounds. This was just a quick look showing the nomenclature system of these molecule. Finally we looked at cis- and trans- isomerism as it applies to rings and alkenes. We took one additional step in describing the Cohn-Ingold-Prelog system of prioritization of substituents to determin if a an alkene is either (E) or (Z), where (E) corresponds to trans- and (Z) to cis-.
- Lecture Date: Tuesday, March 15, 2022
We had a split topic day today. First topic of the day was an introduction to WebMO and computational chemistry. Many of the Co-Op's have a computational chemistry component and WebMO is the application that allows us to complete those exercises. We introduce the server and show how to run some basic jobs. More will be included in the Canvas Shell when that us uploaded. The second topic was stereochemistry. We introduced the topic of enantiomers. We looked at what physically allows for the creation of enantiomers, four different groups attached to a tetrahedral center, and how enantiomers are distinguished by the way they react with plane polarized light. Lot's more to come on stereochemistry.
- Lecture Date: Thursday, March 17, 2022
We dove deeper into stereochemistry today. Today we reviewed how to identify stereocenters, designation of configuration, molecules with more than one streocenter, enantiomers, diastereomers, meso molecules, and different ways to draw enantiomers using mirror images or reversing stereocenters.
- Lecture Date: Tuesday, March 29, 2022
Today we finish stereochemistry with a look at the measurement of optical rotation, explanation of enantiomeric excess, the use of Fischer projections to communicate linear molecules with streocenters, and resolution of enantiomers. We concluded the lecture with a summary of stereochemical notations and definitions of common terms.
- Lecture Date: Thursday, March 31, 2022
We started the energy and mechanism, chapter 6. Today we take a look and enthalpy, entropy, Gibb's free energy, reaction equilibria, reaction rates, energy diagrams, and Hammond Postulate.
- Lecture Date: Tuesday, April 5, 2022
We closed out our look at chapter 6 today with a look at arrow pushing and common mechanistic steps.
- Lecture Date: Thursday, April 7, 2022
And we are on to Chapter 7! Chapter 7 is on substitution and elimination reactions. This is not the hardest material that we will cover in the CHEM 12 series, but it is a litmus test of sorts. This will be our most challenging material to date, and it will require a working knowledge of all the information that we examined previously. Today we take a brief look at nomenclature, some useful terminology, examples of substitution reactions in general, and finally we begin our look at substitution nucleophilic first order (SN1) reaction mechanism.
- Lecture Date: Tuesday, April 12, 2022
Continuing our look at at SN2 reactions, today we use Hammond postulate to understand how the substitution degree of the substrate affects the rate of the chemical reaction. After completing SN2 reactions we move on to SN1. We again use Hammond postulate to exam the rate determining step for the SN1 reactions and find that the rate is governed by the stability of the carbocation intermediates. We look at the factors affecting carbocation stability and then do a couple of examples of reaction competitions that demonstrate using the principles discussed.
- Lecture Date: Thursday, April 14, 2022
Today we really dug in to the SN1 mechanism and the stability of the carbocation intermediate formed during the reaction. We examine the 1,2-hydride shift as well as the 1,2-alkyl shift. In addition, we spend time going over kinetic vs. thermodynamic selectivity in a chemical reaction and stereochemistry.
- Lecture Date: Tuesday, April 19, 2022
We start elimination reactions today. Still in Chapter 7, we move on from the substitution reactions to look at both the E1 and E2 reactions. Here we look at the mechanisms, regioselectivity and stereoselectivity of these reactions.
- Lecture Date: Tuesday, April 26, 2022
We start this lecture with a look at the stereoelectronic effects of the E2 reaction. While operative in all E2 reactions, the stereoelectronic effect plays a very strong roll in cyclohexane derivatives. From there we start a comparison of the SN2/E2, SN1/E1 reaction mechanisms. This part of the lecture is a data intensive presentation of the comparative rates of reaction taken from the literature.
- Lecture Date: Thursday, April 28, 2022
Continuing our look at the SN2, E2, SN1, E1 reaction mechanisms. Here we continue our look at solvent effects, nucleophile, base, and temperature. Today we introduce the magic sheet (a two page document that helps with assessing reactions) and show how to use all the information on it to assess reactions and determine the major product.
- Lecture Date: Tuesday, May 3, 2022
Continuing our look at the SN2, E2, SN1, E1 reaction mechanisms. Today is all about example problems.
- Lecture Date: Thursday, May 5, 2022
Having finished the substitution/elimination chapter 7, this lecture starts with a summary and final overview of the major decision concepts in determining the course of a reaction. We quickly then proceded to chapter 8 and a look at alkenes. Here we address the nomenclature, relative stability, and reactivity of alkenes. We start our look at electrophilic addition reactions to alkenes.
- Lecture Date: Tuesday, May 10, 2022
Today we hit one of my favorite topics, hydroboration-oxidation. While I don't talk about it much, I'm actually a boron chemist by training. My PhD advisor was Bakthan Singaram, who was a postdoc for the Nobel Laureate H.C. Brown. Brown earned the Nobel Prize for the hydroboration-oxidation reaction of alkenes in 1956. All of my PhD work revolved around boron. So today we cover hydroboration and the quirkiness that is boron.
- Lecture Date: Thursday, May 12, 2022
LAST LECTURE!. It's the last lecture. No new content today. Today is just a short video on what to expect for the final exam. Just an overview of the topics covered and exam format. And with that, that's a wrap.