SCH4U Lee 2

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Chemistry

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Jan 9, 2024

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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 ) Unit 2: Organic Chemistry “Common knowledge” Kahoot! In the food industry, “organic” means the product involves no synthetic fertilizers or pesticides. “Organic” means “related to life .” Whether an organic food actually contains more nutrition or less harmful substances depends on each product. In the beginning, organic compounds were believed to be produced only by naturally occurring living organisms. Starting with urea, more and more organic compounds can be synthesized. Now, organic compounds means carbon-based compounds (which very likely also contain H ), which are characteristic to life on Earth. Earth’s crust is not particularly carbon-rich (0.2%), but about half of living organism’s dry mass is carbon. There are two reasons why carbon is so life-friendly. (1) Carbon makes up to 4 bonds. It is capable of making tetrahedral, trigonal planar, and linear shapes. (2) Adequate bond (dissociation) energy. Carbon is small enough so that its bonds do not break easily. It also has a medium electronegativity , so that it does not form hard-to-break ionic bonds with elements on the other end of the electronegativity spectrum. Carbon bonds with a variety of elements. These two properties make carbon a versatile building block. Many carbon-based organic compounds are therefore large and complex. Exercise 0 : Oxygen is the most abundant element in Earth’s crust. Why is oxygen not the best building block for life? Only 2 bonds; forms ionic compounds that are too hard to break Extended topic: Are there silicon-based life? 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 ) https://www.youtube.com/watch?v=fQCrrPohyts Hydrocarbons - Alkane (suffix: -ane ) Hydrocarbons (H & C, nothing else) are the simplest type of organic compounds. And the simplest type of hydrocarbons are alkanes (all names of alkane ends with -ane), which is solely made of sp 3 carbon saturated with hydrogen. Alkanes have the chemical formula of C n H 2n+2 (the “+2” H are attached to the C and both ends). Prefix (# of carbon in the main chain) 1 2 3 4 5 6 7 8 9 10 meth- eth- prop- but- pent- hex- hept- oct- non- dec- Please use 2 minutes to memorize this list. We will play a Kahoot game! Exercise 1 . What should we call C 6 H 14 ? hexane Exercise 2. There may be one or more carbon side chains on a hydrocarbon. Draw one C 6 H 14 that includes a carbon branch - a side chain . If you have a molecular model building kit, build one. How to draw: There are four frequently-seen ways to draw an organic compound: (a) molecular/chemical formula (C 6 H 14 ), (b) condensed structural diagram, (c) line diagram, and (d) full structural diagram. Please draw all of them for your side-chained C 6 H 14 . It turns out there are five possible C 6 H 14 . The straight chain hexane is n- hexane ( n = normal). The other four are: 2- meth yl pentane , 3- meth yl pentane , 2,3- di meth yl butane , and 2,2- di meth yl butane . Can you see the naming pattern here? If the side chain grows on the second carbon of the main chain, add “ 2- ” before the side chain. 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 ) # of the same functional group on a side chain: 2 = di -, 3 = tri -, 4 = tetra - Length of carbon chain in the functional group: 1 = meth yl , 2 = eth yl , 3 = prop yl , 4 = but yl IUPAC (International Union of Pure and Applied Chemistry) is the agency that makes the rules of nomenclature. In this course we will learn several key naming principles. Besides the three rules above, please know that: (1) The longest continuous carbon chain is the main chain. (2) Minimize numbers. 2,2-dimethylbutane is better than 3,3-dimethylbutane. See Google slide for more explanation: https://docs.google.com/presentation/d/1HoLRrlCGU5k-OcGFjVr5cMPsshc5ag6j48uNzueUujU/edit?usp=sharing Exercise 3 . Name as many different C 5 H 12 as you can. (Try to rotate them to see if two apparently different compounds are actually the same.) n-pentane, 2-methylbutane, 2,2-dimethylpropane Finally, name the alkane on the right: 2,2,3,3-tetramethylbutane Isomers You have learned isotopes - same element (same number of protons) but with different numbers of neutrons. Many complex organic compounds have isomers , which share the same chemical formula (e.g. C 6 H 14 ) but are structurally different. We just found out that C 6 H 14 has 5 isomers and C 5 H 12 has 3. Let’s appreciate the number of isomers for different alkanes. https://i.stack.imgur.com/kAbs7.jpg Exercise 4 . Name two isomers of the 8-carbon compound in exercise 3. How many isomers does it have? 3,4-dimethylhexane, 2,2-dimethylhexane Properties of Alkanes Under room temperature (25°C) and 1 atm, methane, ethane, propane, and butane exist as gas. These make up natural gas (the C comes from anaerobically decomposed organisms and 100+ million-year-old organic compounds), in which 3
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