Chapter 12: Alkanes - Organic Chemistry PDF

CHM 2010 CH 12 Stoker CHAPTER 12 Alkanes Organic vs Inorganic Early definitions ...

CHM 2010 CH 12 Stoker CHAPTER 12 Alkanes Organic vs Inorganic Early definitions  Organic compound – compounds that were obtained from living organisms.  Inorganic Compounds – compounds from mineral constituents of the earth. Current definitions  Organic compound – carbon containing compounds and its derivatives  Inorganic compounds – non-carbon containing compounds Organic Chemistry – the study of hydrocarbons and its derivatives.  Approximately 7 million known compounds  No longer from living organisms  Synthesized in the lab Inorganic Chemistry – the study of all other compounds except hydrocarbons and its derivatives.  Approximately 1.5 million known compounds  Almost 5:1 ratio Carbon is Special:  An element that can make such a large number of different compounds 1. Group IVA element  needs 4 electrons for full valence shell 2. MUST have 4 bonds  Combinations to make 4 bonds with predictable geometries 4 single bonds 2 single + 1 double 2 double 1 single + 1 triple Geometry Tetrahedral Trigonal planar Linear linear Tillinger 1|Page CHM 2010 CH 12 Stoker 3. Can bond with other carbons to form long chains and ring structures. Definitions: Hydrocarbon – compounds that only contain carbon and hydrogen.  2 classes o Saturated – contains only single carbon-carbon bonds.  General formula for acyclic alkane = CnH(2n+2) o Unsaturated – contains double and/or triple carbon-carbon bonds.  Lose 2 H’s for every double bond  Lose 4 H’s for every triple bond o Acyclic – all carbons are linked in a single chain  Linear  Branched o Cyclic – carbon atoms are bonded forming a ring structure.  General Formula – lose 2 H’s for Tillinger 2|Page CHM 2010 CH 12 Stoker Simplest Alkanes General #C Expanded Formula Name Formula 1 2 3 4 5 6 Ways to draw structures Structural formula – give information on how the atoms are connected together in the molecule. 1. Expanded form – shows all elements and all bonds. 2. Condensed form – atom groupings are related to specific connection patterns. 3. Skeletal structure or Carbon chain – just shows carbon atoms with no other elements. Understood that carbon will have a total of 4 bonds. Missing bonds are filled with hydrogens to make 4 bonds to each carbon. 4. Line-Angle structure or stick structure – lines are the bonds between carbon atoms. Carbon atoms are the connection points. Expanded Form – shows the connectivity for all atoms in the molecule and the bond types connecting the elements ◦ C5H12 Tillinger 3|Page CHM 2010 CH 12 Stoker ◦ C7H16 Condensed form – atom groupings are related to specific connection patterns. ◦ C7H16 Skeletal structure or Carbon chain – just shows carbon atoms with no other elements. Understood that carbon will have a total of 4 bonds. Missing bonds are filled with hydrogens to make 4 bonds to each carbon. Line-Angle structure (stick structures) – lines are the bonds between carbon atoms. Carbon atoms are the connection points. The number of hydrogen atoms is understood to give carbon 4 bonds total. All other elements are shown in the structure. Tillinger 4|Page CHM 2010 CH 12 Stoker Constitutional Isomers: Constitutional Isomers – different compounds with the same chemical formula.  They have the _________________chemical formula but the atoms are connected ____________________.  More than one structural formula  Begins with C4H10 structures and goes up from there.  The number of isomers grows exponentially as the number of C atoms increases in the molecule. Note: There are different types of isomers. Tillinger 5|Page CHM 2010 CH 12 Stoker Draw the constitutional isomers for 1. C4H10 2. C5H12 3. C6H14 Tillinger 6|Page  CHM 2010 CH 12 Stoker Conformations – the specific 3-D arrangement of atoms in a molecule that results from free rotation about a carbon-carbon single bond.  Free rotation gives rise to multiple shapes of the carbon chain.  These are all the same molecule with different conformations.  Free rotation does not occur with double or triple bonds. Sanc amount of connections without lifting my pen Conformations Which of the following are different molecules and which have different conformations? ⑧ A. 5 same molecule different conformation I 2 3 Y 2 345 formula Lisomers but different connectivity same ⑧ B. ↓ ③ different molecule 5 (connectivity is different) ② 5 , 24 Tillinger 7|Page  A molecule might have multiple names , we are CHM 2010 CH 12 naming them according to IUPAC Stoker Naming Alkanes: "family"name 1. Common names Suffix  There are some that you will become familiar and should know. "ane" X 2. IUPAC naming system for Alkane's  A method for naming all organic compounds. Saturated  You will need to be able to apply to all organic compounds. hydrocarbons  As the semester progresses, we will build on this naming system. Straight Chain Alkanes: CnH(2n 2) +  Just need to know how many carbons are linked in a single chain. n 1[ = IUPAC Chemical #C IUPAC Name Structure Prefix Formula 1 Meth CHy Methane 2 Eth CHo Ethane 3 Prop C3H8 propane 4 but cutlio butane 5 Pent 25Hiz Pentane 6 Hex Cottin Hexane 7 Hept GH - Heptane 8 Oct Coltis Octane 9 Non Catzo Nonane 10 dec Goltzz Decane Tillinger 8|Page  CHM 2010 CH 12 Stoker Names and structures (condensed and stick) Propane Butane Pentane CH2 cr CHy v 1 Hexane Heptane Octane 246 8 W M w 1357 Branched Alkanes IUPAC Rules: 1. Find the longest carbon chain. 2. Identify the branching points. a) Identify the substituents (branches) b) The number of carbons in each branch 3. Give the substituent the lowest number location or number combination. 1. If cannot distinguish, then prioritize alphabetically. 4. List alphabetically in name. IUPAC naming format: All Substituents - parent chain - family name ending 1. Substituent location and name a) Substituent location and name separated by a dash. b) If more than one substituent 1. List alphabetically 2. If substituents are the same a) use prefixes di, tri tetra… to indicate how many substituents are the same. b) not used when alphabetizing c) List each location number and separate location numbers with commas 2. Parent chain – how many carbons 3. Family name ending – “ane” for alkanes Tillinger 9|Page  CHM 2010 CH 12 Stoker Substituent Names: N Point of attachment to parent chain (largest carbon chain) What are the IUPAC name for the following structures? - E General S Strategy -TC's S # * · & I. identify and name parent chain Branching point-substitution ⑧ & 1. ⑨ 2 and 3L. Identify name Parent chain Lepton e 3 = substituents substituent name = M-Ethyl.Combine 3 Ethyl 4 into 4-Ethylheptane = ⑪ one word - ~ 2 I 7 & 2 · & Parent chain = Heptane I ③ 5 30 7 2. Pickth substituent names = 3-methyl and 4-ethyl = methyl - - list them lowest alphabetically - set methyl Ethyl-3-methylheptane. 11. # G ic /methyl 1- * Parent Chain heptane ⑥ = Ethel22 50 < 3 ⑨ 1 substitution = 1- Ethyl and 2-Methyl (2) 3. & · ⑧ 2 T 8 T H- Ethyl-2 2-dimethyl heptane , 3 I ↑ heptone Tillinger 10 | P a g e  # locations CHM 2010 CH 12 methyl 2, 3 , 4 , 5 2,3,4 , 5 methyl and we Stoker & - methyl L > R R + L - - ⑧ * I i some so prioritize y L alphabetically 4. 6 Hexane methyl and Ef & = Ethyl Parent chain Hexane : Substitution : 3- Ethyl-2 , 4, 5-trimethyl name : 3- Ethyl-2 , 4. 5-trimethylhexart Branched Substituents:  High frequency substituents  Named after carbon classification  Only use when no other simpler substituent option exists. Parent chain - L I ↳ S I ↳ 8. A methyl L 2 2 3 - looks like aT - - meth - il I 3 21 I 3 2 longest go chain always takes priority · Ethyl 3c in substitution I 3 e3 2 methyl & "isopropyl" "g - & I 6 * & 7 4-isopropylheptance Tillinger 11 | P a g e  4 , 3, 2 5 6,7 and , L > R CHM 2010 CH 12 - R= L Stoker Secondary Butyl group o Parent chain : Octane ↳ Substitution : = & & n-sec-batyl 3 methehere 17 methyl 8 L.5 6 & - & 5 · Methyl 7 3 3-methyl methyl I · k 2 Y 3 I Qg Methyl · & · em ethyl I * 6-tetramethylhectone 2-methyl Ethyl-2 2 6 alphabet goes first - 3- , , , First in 4-sec-butyl-2 3-dimethyl Octane ma name : , Carbon Classification: Based on the number of carbon atoms bonded to the carbon atom of interest.  Primary carbon (1) – has only 1 carbon atom bonded to it. [Iline] o The rest of the atoms are hydrogens. o Usually found at the end of a carbon chain. · o CH3 group  Secondary carbon (2) – has 2 carbon atoms bonded to it. o CH2 group [2 lines) ,a  Tertiary carbon (3) – has 3 carbon atoms bonded to it. 13 lines) o CH group  Quaternary carbon (4) – has 4 carbon atoms bonded to it. - o A carbon atom with NO hydrogens attached. [Y lines Im5 T Classify the carbons in the following structure. 10 · · 10 yo * 2 · · 10 10 30 20 d 20 20 10 all end C's are primary Tillinger 12 | P a g e CHM 2010 CH 12 Stoker Cycloalkanes = cyclic compounds. Cycloalkane – a saturated hydrocarbon with a ring structure (cyclic arrangement)  Minimum number of carbons is 3 in ring  Range 3 – 30 carbons  General formula CnH2n cycloalkones = CnHan + 2 = Acyclicalkanes 3 carbons 4 carbons 6 carbons ~ 5 carbons tetrahedral geometry = 109. 5 3 and 7 are unstable [membered rings) because of strain bands less tran 109 5 ring ,. 5 and 6 · stable structures (band angle of 109. 5) - - · prominent in biomolecules unsubstituted cycloalkanes = all CHz (2% branched cycloaltiones Just = branching one CH or IUPAC Naming of Cycloalkanes (3% E (49) Use the same general guidelines as naming straight- and branched-chain alkanes.  The parent chain uses the number of carbons in the ring structure. parent chain =.  Substituent location number depends on the number of substituents o 1 substituent – no number needed.  There is no C#1 in a circle, therefore understood that the substituent is C#1. o 2 substituents – alphabetical priority determines C#1.  Numbering of C’s follows in the direction to give the lowest location numbers to the other substituent. o 3 or more substituent – lowest number combination or if needed alphabetical priority. Tillinger 13 | P a g e  1. nameParent chain. name 2 substituents CHM 2010 CH 12 3 Stoker What is the IUPAC name for the following structure. o -Isopropyl name - isopropyl cyclohexane & Fo - & substitute no location 8 so * only are : g & 1. & - cyclohexane · in the direction Methyl Parent name : cyclopenture go D rearest of the · substituents : 1-ethyl and 2-methyl substituent 506 -methylcyclopentane [2 1) 85 2. Ethyl name. , M · 3 · cyclopentane thy metht my Parent : · 3. I 2 butyl 1 1- dimethylcycloteptune name - T , 407 38 b 40 - 3. 7 6 Isomers of cycloalkanes Two Types 1. Constitutional isomers – same chemical formula but connectivity of atoms is different. C5H10 cycloalkane isomers Other isomers of C5H10 Yo / 2 CH3 3 ~ 2 E CHz CH I, 1-di... 3 CHz CH2 cycloproport 1, 2-dimethyl Tillinger To identify duplicate structures : 14 | P a g e name using 14A  CHM 2010 CH 12 Stoker 2. Cis/Trans isomers – the same chemical formula with same connectivity, but different 3-D arrangement in space. 1. Because the carbon atoms are held in a fixed location (lack free rotation) in a ring structure, the atoms or groups of atoms attached to the carbons in the ring will have a set configuration based on their attachment. Creates a top and bottom in the structure. 2. These are called “stereoisomers” Same side = (is 000 · opposite sides  Cis – when the substituents are on the same side of the ring. "Trans"  Trans – when the substituents are on opposite sides of the ring. o Occurs in rings of all sizes. o Requires 2 substituents on 2 different carbons. o Substituents do not need to be the same o Biochemically important. o This nomenclature is limited to ring structures that contain one hydrogen and one substituent on the substituted carbon atoms. (more complicated systems use E,Z nomenclature system.) Identify isomers as cis/trans and then name the stereoisomers. cyclohexane cyclohexane 2 3 ↑ 1. ↑ same side ↑ = "Cis" 2. opposite sides = "Trans" trans-1 3-dimethylcyclohexane sig-dimethylcyclohexane - , methyl cyclopentore Ethel ' 2 Ibelow. 3. V 4. rons-1-Ethyl-2-methyl cyclopentare -- Tillinger 15 | P a g e CHM 2010 CH 12 Stoker Properties of Alkanes * odor odorless 1. Insoluble in water (polar) =  Hydrocarbons are nonpolar. color-colorless 2. Density is less than water  Range from 0.6 – 0.8 g/mL  Float on top of water &-Alkare danite 3. Boiling points  Lowest boiling points and melting points of all organic compounds  Phases at room temperature. o C1 – C4 are gases o C5 – C17 are liquids o C17 will be solids  As molar mass increases the boiling point increases.  Branched alkanes have lower boiling points because of decreased surface area contact.  Cycloalkanes have higher boiling points than straight chain alkanes due to better packing of particles to create crystal structure. Reactions of Alkanes 2 types of reactions 1. Combustion reactions (react w/ O2) 2. Halogenation reactions (react w/ halogens)  Least reactive of all classes of organic compounds. Tillinger 16 | P a g e CHM 2010 CH 12 Stoker Combustion Reactions A substance reacts with molecular oxygen to produce carbon dioxide and water.  General products o Carbon dioxide and water  General reaction  Exothermic reaction (releases heat)  Product of incomplete combustion is carbon monoxide (CO) Halogenation Reactions A halogen (F, Cl, Br or I) is incorporated into a molecule.  Substitution reaction – remove an atom or group of atoms is replaced by another atom or group of atoms. o For alkanes a hydrogen is removed and replaced with a halogen.  The general reaction is: R-CH3 + X2 R-CH2X + HX o Requires a catalyst o R = the rest of the molecule.  Which can be H, methyl group, ethyl group… o X = halogen atom  Halogenation reactions form a mixture of products. o Not limited to the removal of a specific hydrogen. o Any hydrogen can be removed. o Major product formed based on stoichiometry (still a mixture.) Tillinger 17 | P a g e  CHM 2010 CH 12 Stoker Mixture of Products  Ratio of alkane to halogen determines how many halogens will incorporate into the alkane. 1 mole CH4 + X2 CH3X + HX 2 mole CH4 + 2 X2 CH2X2 + 2 HX 3 mole CH4 + 3 X2 CHX3 + 3 HX 4 mole CH4 + 4 X2 CX4 + 4 HX  As the number of carbon atoms increases, the number of possible isomers increases. ◦ e. g. ethane (CH3CH3) + ? mole Cl2  multiple products HH 1 ↓ H - C - C - H + C 2) - - it it ( - c) -I L CzHo + 3Cz < [Hz(y 3HC + - 63 : Tillinger 18 | P a g e CHM 2010 CH 12 Stoker -methyl Naming Halogenated Alkanes: Ethyl ·  Rules are the same as for other alkanes  Halogen is a substituent  Prioritized like other alkyl substituents ◦ Location number or alphabetical ◦ Substituent names for halogens 8-methyl =  fluoro = F 2 - Ethyl-1 4-dimethylcydooctane ,  chloro = Cl  bromo = Br  iodo = I Name the following molecules. name : 3-bromo-n-ethyl heptone I 23 n56 is 1. 6-bromo-2-chloro-5 Ethyloctane Ethyl name - - 8565432'Octare * 2. bromine - chlorine 6 2 ↑ 5 3 name : 1 - Ethyl-3-florocycloteptanc - 2 6 I 7 3. Tillinger 19 | P a g e  heavier CHM 2010 are CH 12 Stoker Properties of halogenated alkanes - - -  Higher boiling points than similar alkanes ◦ The C – X bond is more polar than a C – H bond. (dipole-dipole - - ◦ Dipole – dipole interactions versus just London Dispersion Forces -- ◦ Higher MW Hydrocarbons  Higher densities than alkanes ◦ The higher mass of the halogen atoms.  Haloalkanes with 2 or more Cl, Br, or I have densities greater than water. Carbon tetrachloride &S Water CCIn (Heavier than water cause it has a halogen - ~ a Just Carbons(Hydrocarb ↳ & - water Tillinger 20 | P a g e