introduction to organic chemistry

what is organic chemistry

the chemistry of carbon compounds

life on our planet is based on____

carbon

what does organic mean

to do with living beings

nowadays, many carbon based materials like plastics and drugs are made…

synthetically and there are large industries based on synthetic materials

how many compounds or carbon are known

well over 10 millions, far more than those of all other elements put together

what is special about carbon

it can form rings and very long chains which may be branched

why can carbon form rings and very long chains which may be branched

• a carbon atoms has 4 electrons in its outer shell so forms four bonds

• a carbon carbon bond is relatively strong and non polar

strength of carbon carbon bond

347 kJ mol-1

carbon hydrogen bond strength

414 kJmol-1

carbon hydrogen bonds are similar to carbon carbon bonds in the sense that they are….

also strong and relatively non polar

hydrocarbon chains form the skeleton of…

most organic compounds

in all stable carbon compounds how many covalent bonds can carbon form

four and has 8 electrons in its outer shells

ways carbon can form 4 bonds

• four single bonds

• two single bonds and a double bond

• one single bond and one triple bond

types of formulae of carbon compounds

• empirical

• molecular

• displayed

• structural

• skeletal

• 3D

what is empirical formula

a formula that shows the simplest ratio of the atoms of each element present in a compound

what is molecular formula

the formula that shows the actual number of atoms of each element in the molecule

how is molecular formula found

• the empirical formula

• the relative molecular mass of the empirical formula

• the relative molecular mass of the molecule

why are other types of formula used in organic chemistry

because compared with inorganic compounds, organic molecules are more varied

the type of formula required depends on…

the information that you are dealing with

you may want to know about the atoms are…

arranged within a molecule aswell as just the number of each atom present

what is displayed formula

this shows every atom and every bond in the molecule

what is structural formula

shows the unique arrangement of atoms in a molecule in a simplified form, without showing all the bonds

each carbon is written separately, without the atoms or groups that are attached to it

in structural formula, what are branches shown in

brackets

when is skeletal formula used

with more complex molecules displayed formulas become time consuming to draw

in skeletal notation, the carbon atoms are…

not drawn at all

what do straight lines represent in skeletal formula

carbon carbon bonds and carbon atoms are assumed to be where the bonds meet

neither ____ nor ______ are drawn in skeletal formula

hydrogen atoms not C-H bonds

in skeletal formula, each carbon is assumed to form…

enough C-H bonds to make a total of four bonds (counting double bonds as two)

what does skeletal formula give a rough idea of

the bond angles

bond angle in an unbranched alkane chain

109.5

what are 3D structural formulae

these attempt to show the 3D structure of the molecule

bonds coming out of the paper are shown by wedges

bonds going into the paper are shown by dotted lines

types of reaction mechanisms

• curly arrows

• free radicals

you can often explain what happens in organic reaction by considering…

the movement of electrons

as electrons are negatively charged the tend to…

move from areas of high electron density to more positively charged areas

example of electrons in high density areas moving to more positively charged areas

a lone pair of electrons will be attracted to the positive end of a polar bond

what is a curly arrow used to show

the movement of a pair of electrons

what shows the movement of a pair of electrons

a curly arrow that starts from a lone pair of electrons or from a covalent bond and moves towards a positively charged area of a molecule to form a new bond

sometimes a covalent bond consisting of a pair of electrons shared between two atoms may break…

in such a way that one electron goes to each atom that originally formed the bond

these fragments of the original molecule have an unpaired electron and are called free radicals

free radicals are usually…

extremely reactive

what was the system for naming compounds developed by

IUPAC

what is IUPAC

an international organisation of chemists that draws up standards so that chemists throughout the world use the same conventions, like a universal language

systematic names tell us about…

the structures of compounds rather than just the formula

what is a root

a systematic name has a root that tells us the longest unbranched hydrocarbon chain or ring

what does the syllable after the root tell us

if there are any double bonds

-ane means there are ____ double bonds

no

-ene means there is ____ double bond

one

prefixes and suffixes describe…

the changes that have been made to the root molecule

side chains are shown by a….

prefix whose name tells us the number of carbons

example of prefixes added to root

• methyl

• ethyl

• propyl

• butyl

what additional prefix is given to hydrocarbon rings

cyclo

suffixes are added to the ____ of the root

end

example of suffixes added to the root

-ol

what are functional groups

the one or more reactive groups that are attached to the hydrocarbon chain

functional groups act in the same way….

whatever the length of the hydrocarbon chain

suffix of aldehyde

-al

suffix of ketone

-one

suffix of carboxylic acids

-oic acid

halogenoalkanes are named using…

a prefix such as chloro rather than a suffix

what is R usually used to represent

a hydrocarbon chain of any length

what does eth represent

indicated that the molecule has a chain of two chain atoms

what does prop indicate

a chain of three carbon atoms

what does meth indicate

a single carbon

what does an indicate

there’s are no double bonds

with longer chains, you need to say where a ______ is located on the main chain

side chain or functional group

what is a number/locant used to tell us

the position of any branching in a chain and the position of any functional group

what are structural isomers

hydrocarbon chains that have the same molecular formula but different structural formulae

the _____ combination of numbers is always used

smallest

what happens if a molecule has more than one functional group

the groups are put in alphabetical order rather than numerical order

examples of how to show you have more than one of the same substituting group by adding prefixes aswell as functional groups

• di

• tri

• tetra

what is a homologous series

a family of organic compounds with the same functional group but different carbon chain length

members of a homologous series have a…

general formula

general formula of alkanes

CnH2n+2

alkene general formula

CnH2n

features of homologous series

• members of a series have same general formula

• each member of series differs from the next by CH2

• length of carbon chain has little effect on chemical reactivity of functional groups

• length of carbon chain affects physical properties like melting point boiling point and solubility

• melting and boiling points increase by a small amount as the number of carbon atoms in the chain increases due to increased intermolecular forces

• chain branching generally reduces melting points because molecules pack together less well

in general small molecules are …. and larger ones are ….

gases

liquids or solids

what are isomers

molecules that have the same molecular formula but whose atoms are arranged differently

what are the two basic types of isomerism in organic chemistry

• structural

• stereoisomerism

structural isomers definition

hydrocarbon chains having the same molecular formula but different structural formulae

3 subdivisions of structural isomers

• they can have the same functional groups attached to the main chain at different points (positional)

• functional groups that are different (functional group)

• a different arrangement of the hydrocarbon chain such as branching (chain)

what is positional isomerism

the functional group is attached to the main chain at different points

what is functional group isomerism

there are different functional groups that the molecular formula could represent

what is a chain isomer

the hydrocarbon chain is arranged differentl

chain isomers are sometimes called….

chain branching isomers

the existence of isomers makes the task of identifying an unknown organic compound….

more difficult

why do isomers make the task of identifying an unknown compound more difficult

• because there may be a number of compounds with different structures that all have the same molecular formula

• so you have to use analytical methods that tell you about structure

what is stereoisomerism

where two or more compounds have the same structural formula and differ in the arrangement of the bonds in space

two types of stereoisomers

• E-Z isomerism

• optical isomerism

what does E-Z isomerism tell us about

the positions of substituents at either side of a carbon carbon double bonds

the two substituents on an E-Z isomer may either be on:

• the same side of the bond Z (cis)

• or on opposite sides E (trans)

if the two substituents are on the same side of the bond….

it’s a Z, cis

if the two substituents are on opposite sides of the bond…

it’s E trans

substituted groups joined by a single bond can…

rotate around the single bond so there are no isomers but there is no rotation around a double bond

as there is no rotations around a double bond….

Z and E isomers are separate compounds and are not easily converted from one to the other

what does E-Z come from

the German Entegegen (opposite-trans) and Zusammen (together-cis)