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Organic Chemistry Lesson 1 Homologous Series We Are Here Lesson 1: Homologous Series Objectives: Reflect on previous knowledge of organic chemistry Understand the term ‘homologous series’ Conduct the fractional distillation of crude oil Understand and use a variety of different types of formula used in organic chemistry Reflecting on Organic Chemistry What is the definition of organic chemistry? What do you remember about organic chemistry from IGCSE? What is the value of learning organic chemistry? Organic Chemistry Organic chemistry is the chemistry of carbon containing compounds. From the very simple: methane To the very complex: Haem B Homologous Series A homologous series is a family of compounds that differs only by the length of its hydrocarbon chain (i.e. the number of CH2 units in the main carbon chain). Members are usually listed in order of increasing size. Members share: General formula Chemical properties Three such series are the: Alkanes Alkenes Alcohols Homologous Series and Properties What do you think will be the trend in melting/boiling points as you go down a homologous series? Why? Name Molecular Formula Melting Boiling Point Point C C State at 25C Methane CH4 -183 -164 gas Ethane C2H6 -183 -89 Propane C3H8 -190 -42 Butane C4H10 -138 -0.5 Pentane C5H12 -130 36 Hexane C6H14 -95 69 Heptane C7H16 -91 98 Octane C8H18 -57 125 Nonane C9H20 -51 151 Decane C10H22 -30 174 Undecane C11H24 -25 196 Dodecane C12H26 -10 216 Eicosane C20H42 37 343 Triacontane C30H62 66 450 liquid solid Fractional Distillation of Crude Oil (25 mins) Crude oil is the main feedstock for producing organic compounds Complete the fractional distillation of crude oil experiment here. Fully explain all your observations Formulas Draw the compound with the formula C4H8O What did you get? Clearly a molecular formula is not enough! Types of Formula Empirical Formula C4H8O C4H8O Molecular Formula C4H8O C4H8O Full Structural Formula Condensed Structural Formula Aka displayed formula Note the ‘=‘ used for the C=C double bond CH2=CHCH2CH2OH Skeletal formula Not required but v. useful Used in data booklet for complicated structures Do not use in exam answers! CH2=C(CH3)CH2OH Thinking About Formulas Produce a table to summarise each of the formulas. Include columns for: What they show Pros Cons How you make them Draw full structural, condensed structural and skeletal formulas for at least 5 of the C4H8O compounds (not the cyclic ones) Key Points Organic chemistry is the chemistry of carbon containing compounds A homologous series is a family of organic compounds differing only by the length of their carbon chains The melting and boiling point increases as you go down a homologous series Displayed formulas show the unambiguous arrangement of atoms in a compound