SCH4U Lee 2.6

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OCV Chemistry, Grade 12 University Preparation (SCH4U-04/05) Ottawa-Carleton Virtual Secondary School 2020-2021 Mr. Daniel Cho-En Lee ( daniel.cho-en.lee@ocdsb.ca ) Aldehyde (suffix: -al ) and Ketone (suffix: -one ), =O is a carbonyl group Both aldehydes and ketones have the C=O carbonyl group. If the carbonyl group is bonded to a C that is at the end of a chain, it is an aldehyde (similar to primary alcohol). If the carbonyl group is bonded to a C that is in the middle of a chain, it is a ketone (similar to secondary alcohol). Hydrogen bonds? While the carbonyl O is very δ - , there is no H attached to O like an alcohol. Lacking a very δ + H, aldehydes and ketones cannot form hydrogen bonds with each other. (They can still form H-bond with water, because water has a very δ + H.) The simplest aldehyde is methan al (old: formaldehyde), while the simplest ketone is propanone (old: acetone). It is not necessary to specify butan-1-al because there can be no other way. Likewise, it is not necessary to specify propan-2- one. Exercise 1. What is the molecular formula of propanal, propanone, propan-1-ol, and methoxyethane? C 3 H 6 O, C 3 H 6 O, C 3 H 8 O, C 3 H 8 O Exercise 2. Among ethanal, ethanol, and ethoxyethane, which has the lowest molar mass? Example: CH 4 molar mass = 12 + 4x1 = 16 g/mol ethanal < ethanol < ethoxyethane Exercise 3. Rank the solubility of water of the following: hexane, hexan-2- one , and hexan-1- ol . Explain. Alcohol (has δ + H) > ketone > alkane Exercise 4. Rank the boiling point of the following: butane, butan-1- ol and butan al . Explain. Alcohol (hydrogen bonds) > aldehyde > alkane Methanal (formaldehyde) in embalming fluid Watch: https://youtu.be/9cTVn30XSeE 1

OCV Chemistry, Grade 12 University Preparation (SCH4U-04/05) Ottawa-Carleton Virtual Secondary School 2020-2021 Mr. Daniel Cho-En Lee ( daniel.cho-en.lee@ocdsb.ca ) The embalming fluid is actually a mixture of methanol, methanal, and some other aldehyde. Similar to how alcohol- based hand sanitizers kill germs, these not-so-polar solvents disrupt the intermolecular interactions of biomolecules, such as proteins, of decomposing microorganisms. Therefore, the body is preserved in a sterile environment. Propanone (acetone), a useful organic solvent While miscible in water, propanone’s 3-carbon backbone is also non-polar enough to dissolve non- polar compounds, such as the dye of permanent marker and nail polish. Propanone is a reactant of many industrial reactions. The toxicity of acetone is low. (Everything is toxic with enough dose, the real question is - how much is too much?) Exercise 5. While touring an anatomy lab, you noticed a “morgue stench.” It does not smell like alcohol or bleach, or any putrid decaying matter. What do you think is the chemical that contributes to the smell? Methanal (plus methanol) Exercise 6. You accidentally wrote on a white board with a permanent marker (non-polar). Which liquid do you think will work the best to remove the ink? (a) water, (b) hand sanitizer gel, (c) nail polish remover. Propanone (does not have hydrogen bond, can incorporate the largely non-polar ink) Carbonyl groups on sugar Glucose: 2,3,4,5,6-penta hydroxy hexan al , fructose: 1,3,4,5,6-penta hydroxy hexan-2- one Carbohydrates are very common and important biomolecules. (There are only four main categories: lipids, carbohydrates, proteins, and nucleic acids). Each molecule of glucose and fructose contains one carbonyl group and multiple hydroxyl groups in their less stable linear form. In the more stable ring form, the carbonyl group becomes an “ether-like” (R 1 -O-R 2 ) linkage while the hydroxyl group remains. 2

OCV Chemistry, Grade 12 University Preparation (SCH4U-04/05) Ottawa-Carleton Virtual Secondary School 2020-2021 Mr. Daniel Cho-En Lee ( daniel.cho-en.lee@ocdsb.ca ) Exercise 7. Use the table below to compare and contrast the structure of glucose vs. fructose in their linear form and ring form. glucose fructose Linear form The carbonyl group is a(n) … What is its IUPAC name? Aldehyde See above Ketone See above Ring form How many atoms form the ring? 6 (5 C, 1 O) 5 (4 C, 1 O) Molecular formula C 6 H 12 O 6 C 6 H 12 O 6 Carbonyl group on caffeine Many organic compounds that have a carbonyl group, such as caffeine. Here, the C=O carbon is sp 2 hybridized, and so are the other carbons. Each nitrogens on the ring also have three electron densities coming out of it (sp 2 , the other two electrons are the π bond without the double bond!). So C=O is co-planar with the rest of the molecule. The only exception are the hydrogens on each of the sp 3 methyl side chains. Watch: Your brain on caffeine https://youtu.be/4YOwEqGykDM Exercise 8. Which biomolecule does caffeine mimic in the brain? adenosine Oxidation and Reduction of aldehyde Previously, we learned that primary alcohols can be oxidized to aldehyde, while secondary alcohols can be oxidized to ketones. Out of the two carbonyl functional groups, only aldehyde can be further oxidized to carboxylic acid. Oxidation means the removal of electrons. As the central C makes more bonds with oxygen and less bonds with H, it becomes increasingly less δ - and more δ + . 3

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OCV Chemistry, Grade 12 University Preparation (SCH4U-04/05) Ottawa-Carleton Virtual Secondary School 2020-2021 Mr. Daniel Cho-En Lee ( daniel.cho-en.lee@ocdsb.ca ) The reverse reaction of the oxidation reaction is called a reduction reaction . As less oxygen is bonded with C, the C becomes more δ - and less δ + . (The positive charge is reduced .) A carboxylic acid may be reduced to an aldehyde. An aldehyde may be reduced to a primary (1º) alcohol. A ketone may be reduced to a secondary (2º) alcohol. Exercise 9. Complete the following reactions. (a) ethan al + [R] → ethanol (b) propan one + [R] → propan-2-ol (c) 2-methylbutan-2-ol + [O] → no reaction (3º alcohol, no C-H to lose) Carboxylic Acids (suffix: ... oic acid ) -COOH is the carboxyl group Exercise 1 : How many medium-strong δ + are there in an ethanoic acid molecule? (2, H and C) How many medium-strong δ - lone pairs are there on an ethanoic acid molecule? (4, 2 from each O) Do the same analyses for ethanol. (δ + : 1 from H, δ - : 2 from O) The boiling points of ethanoic acid tend to be high, because there are multiple hydrogen bonding / dp-dp interactions coming out of their polar groups. 4

OCV Chemistry, Grade 12 University Preparation (SCH4U-04/05) Ottawa-Carleton Virtual Secondary School 2020-2021 Mr. Daniel Cho-En Lee ( daniel.cho-en.lee@ocdsb.ca ) Exercise 2: Rank the boiling point of the following molecules (without looking it up): ethanoic acid, ethanal, ethanol, and ethene Carboxylic acid > alcohol > aldehyde > alkene End of Quiz #6 coverage You need to know the names and structures of aldehyde, ketones, and carboxylic acid and their derived properties such as boiling point and solubility in water. Don’t worry about real-world examples and applications. SCH4U-6 Quiz #6 https://docs.google.com/presentation/d/1S4KWlEi9eFBitfrcWzs7EY9XXTjWD-BK-iCEdeRBZ2w/edit?usp=sharing SCH4U-6 Quiz #7 https://docs.google.com/presentation/d/15LdhO1tJ0I8jTRK_lAYDa0esZfd8QuPfWlqazTBHrvc/edit?usp=sharing Carboxylic acid in water Being very miscible with water (up to a certain chain length, of course), carboxylic acid is the most common type of organic acid. In a 1M (M = mol/L) solution, the H on the carboxyl group has a small chance, about 1 in 250 under neutral pH, of dissociating. (Unit 4) The H + joins water to form, H 3 O + , hydronium ion. The rest of the molecule, now a negatively charged ion, is called ... oate , such as methanoate (old: formate) and ethanoate (old: acetate). Because only a low ratio of the acid is actually dissociating, carboxylic acids are all weak acids. (HCl in water is a strong acid, as the dissociation is nearly 100%.) R-COOH (aq) + H 2 O (l) ⇌ H 3 O + (aq) + R-COO - (aq) Carboxylic acids in vinegar and soft drinks H 3 O + gives us the “sour taste.” Many common sour tastes of our food come from carboxylic acids. For example, vinegar is 5% ethanoic acid . Despite being “weak”, pure acetic acid is still too reactive/corrosive as a drink. Exercise 3. Suppose there are multiple ingredients in a bottle of vinegar. How is vinegar “distilled”? Estimate the temperature required to produce “distilled” vinegar (5% ethanoic acid & 95% water). bp water = 100ºC bp ethanoic acid = 118ºC Step 1: heat up solution to 100ºC - boil off small organic compounds and water Step 2: heat up solution to 118ºC - ethanoic acid starts to boil - collect Coffee Flavour Wheel 5

OCV Chemistry, Grade 12 University Preparation (SCH4U-04/05) Ottawa-Carleton Virtual Secondary School 2020-2021 Mr. Daniel Cho-En Lee ( daniel.cho-en.lee@ocdsb.ca ) Take a look at the organic molecules you can find in coffee. Humans can differentiate the smell of a few common carboxylic acids. Draw some of the carboxylic acids mentioned above. The reason that traditional instant coffee does not smell/taste so good, is that chemicals with lower boiling points (= easily becomes gas = easily smelled by us) have evaporated during the heat-drying of the instant coffee powder. The more recent instant coffee dried in a -30ºC (near) vacuum so that while water evaporates, many tasty/fragrant organic compounds remain. Citric acid is found in citrus fruits (e.g. orange, lemon) and a very common additive in the food industry. This carboxylic acid is also famous for bearing the name sake of the most important cyclic 6

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OCV Chemistry, Grade 12 University Preparation (SCH4U-04/05) Ottawa-Carleton Virtual Secondary School 2020-2021 Mr. Daniel Cho-En Lee ( daniel.cho-en.lee@ocdsb.ca ) metabolic pathway. There are three carboxyl groups and a hydroxyl group on a citric acid. (4U Biol: how many carbons are there?) For 4U chemistry we do not have to remember any of the above! However, you should know that citrate is the positively charged ion, after citric acid loses 1 or more of its H + . 7

OCV Chemistry, Grade 12 University Preparation (SCH4U-04/05) Ottawa-Carleton Virtual Secondary School 2020-2021 Mr. Daniel Cho-En Lee ( daniel.cho-en.lee@ocdsb.ca ) Exercise 4 (there is no need to memorize - you will be given their structures): ❏ What are the functional groups on a pyruvate (and how many carbons?) Ketone, carboxylic acid, 3 carbons ❏ How many carbons are on an acetyl? (Hint: how many carbons are on an acetic acid?) 2, 2 ❏ Let’s follow through the gaining and losing of functional groups through the citric acid cycle. Carboxylic acid in Fatty acid, Omega-3 Previously we learned that fat contains a large amount of non-polar hydrocarbons, which may pack more or less tightly depending on the conformation of C-C and C=C. But we also say “fatty acid.” Fatty acid and glycerol (propane- 1,2,3-triol) are the two components of fat. Each fat molecule is made of 1 glycerol and 3 fatty acids. Each fatty acid has a carboxylic head and a long, non-polar C-C/C=C tail that is about 20 carbons long. Among many possible fatty acids, there is the “omega-3” class that is frequently marked as a healthy food supplement. The “omega” means “counting from the end”, while “3” means there is a (cis) double bond on the 3rd carbon, counting from behind. These curly fatty acids, due to their multiple cis double bonds, enhance structural fluidity to the lipids they will be incorporated into. The lipids can go on a cell membrane of brain neurons. 8

OCV Chemistry, Grade 12 University Preparation (SCH4U-04/05) Ottawa-Carleton Virtual Secondary School 2020-2021 Mr. Daniel Cho-En Lee ( daniel.cho-en.lee@ocdsb.ca ) Omega acids typically have names like EPA and DHA. These are actually acronyms of their IUPAC names! Take a guess, how many cis double bonds may be found in a DH A? (how about trans double bonds?) Omega-3 fatty acids may be found in fish oil and plant seed oil. These unsaturated fatty acids are often lost (addition reaction on the double bond) when the food is heated up, such as in a deep-frying basin. If you like fish, don’t fry it! Canned fish also has poor omega-3 content. That is why they are marked as a healthy food supplement. Exercise 5 . What is an “omega-3” fatty acid? Why is it a healthy food supplement? There is a double bond on the 3rd last carbon. (There are more double bonds along the chain) The “hook” shape as a result of multiple cis-double bonds enable an usually loose packing of hydrocarbon tails. Omega-3 fatty acid is considered healthy for the roles they play on the cellular membrane (more on the next section). Besides being the end point of the oxidation of alcohols and aldehydes (or the starting point of the reduction reactions to produce the above), a carboxylic acid may be involved in a condensation reaction with an alcohol to produce an ester . A carboxylic acid can also undergo a condensation reaction with an amine to produce an amide . We will discuss them in their respective sections. Carboxylic acids are cheesy Many carboxylic acids smell bad. Vinegar (5% ethanoic acid) has a pungent smell. Butanoic acid gives a distinctive rotten cheese smell. A good portion of our body odor comes from carboxylic acids. Our body does not secrete the 9

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OCV Chemistry, Grade 12 University Preparation (SCH4U-04/05) Ottawa-Carleton Virtual Secondary School 2020-2021 Mr. Daniel Cho-En Lee ( daniel.cho-en.lee@ocdsb.ca ) organic acid directly, but the fat/oil that are made from carboxylic acid, in order to keep prevent water loss. The bacteria that live on our skin utilize these fatty nutritions and break them down, back to fatty acids. Watch: https://youtu.be/g96z1P3z5yU Kahoot! 10