Chapter 14 : Introduction to organic Chemistry Flashcards
Definitions , key ideas and formulae
Definition of hydrocarbons :
●a compound made up of carbon and hydrogen only.
Definition of empirical formula:
●it tell us the simplest whole number ratio of the different types of atoms present in a molecule
Definition of molecular formula :
● this formula shows us the actual numbers of each type of atom in a molecule
Definition of structural formula :
● this formula tells us about the atoms bonded to each carbon atom in an organic molecule e.g. CH3CH=CH2
Definition of displayed formula :
● a drawing of a molecule that shows all the atoms and bonds within a molecule
Definition of skeletal formula :
●a simplified version of the displayed formula that has symbols for carbon and hydrogen atoms removed , as well as the carbon to hydrogen bonds. The carbon to carbon bonds are left in place as are the bonds to other atoms.
Definition of functional group :
● an atom or group of atoms in an organic molecule that determine the characteristic reactions of a homologous series.
Definition of general formula :
● a formula that represents a homologous series of compounds using letters and numbers. By substituting a number for n in the general formula you get the molecular formula of a particular compound in that homologous series.
E.G. General formula for alkanes is Cn H2n+2
Definition of single covalent bonds
●A shared pair of electrons bonding two atoms together
Definition of Sigma bonds
Single covalent bonds, formed by ‘ end-on ‘ overlap of atomic orbitals .
Definition of pi bonds
Multiple covalent bonds involving the sideways overlap of p orbitals
Definition of structural isomers
Compounds with the same molecular formula but different structural formulae.
Definition of stereoisomerism :
Compounds whose molecules have the same atoms bonded to each other but with different arrangements of the atoms in space.
Definition of free radicals
Very reactive atom or molecule that has a single unpaired electron.
Definition of Initiation step:
The first step in the mechanism of free- radical substitution of alkanes by halogens. It involves the breaking of the halogen-halogen bond by UV light from the sun.
Definition of termination step
The final step in a free-radical mechanism in which two free radicals react together to form a molecule.
Definition of the propagation step
A step in a free-radical mechanism in which the radicals formed can then attack reactant molecules generating more free radicals, and so on.
Definition of carbocation
An alkyl group carrying a single positive charge on one of its carbon atoms, e.g +CH2CH3
Definition of electrophile
A species that can act as an acceptor of a pair of electrons in an organic mechanism
Definition of a nucleophile
A species that can act as a donor of a pair of electrons
Definition of an addition reaction
An organic reaction in which two reactant molecules combine to give a single product molecule.
Definition of an elimination reaction
A reaction in which a small molecule, such as H2O or HCl, is removed from an organic molecule.
Definition of a substitution reaction
A reaction that involves the replacement of one atom, or group of atoms, by another.
Definition of hydrolysis
The breakdown of a compound by water, which is often speeded up by reacting with acid or alkali.
Definition of oxidation reaction
The addition of oxygen, removal of electrons or increase in oxidation number of a substance ; in organic Chemistry refers to a reaction in which oxidation is added to a molecule and/or hydrogen atoms are removed from a molecule.
Definition of reduction reaction
The removal of oxygen, addition of electrons or decrease in oxidation number of a substance; in organic Chemistry it is the removal of oxygen atoms from a molecule and/or the addition of hydrogen atoms to a molecule.
What five types of formulae do you get ?
- Empirical formula
- Molecular formula
- Structural formula
- Displayed formula
- Skeletal formula
Name the seven types of homologous series
- Alkanes
- Alkenes
- Alcohols
- Carboxylic acids
- Carbonyl Compounds, namely : aldehydes and ketones
- Esters
- Halogenoalkanes
What is a homologous series?
A group of organic compounds with the same functional group
What is the general formula for alkenes?
CnH2n
What is the general formula for alkanes ?
CnH2n+2
What is the general formula for arenes?
C6H5-
General formula for a halogenoalkane, where x =F, Cl, Br, I
CnH2n+1X
General formula for an alcohol
CnH2n+1OH
General formula for an aldehyde
CnH2n+1CHO
General formula for a ketone
CnH2n+1 COCm H2m+1
General formula for a carboxylic acid
CnH2n+1COOH
General formula for an ester
CnH2n+1 COOCm H2m+1
General formula for an amine
CnH2n+1NH2
General formula for a nitrile
CnH2n+1CN
Functional group for alkenes
C=C
Functional group for an halogenoalkane
A halogen F,Cl, Br, I
Functional group for an alcohol
OH
Functional group for a aldehyde
-C=O
\
H
The functional group for a ketone
C-C=O
\
C
Functional group for a carboxylic acid
-C=O
\
OH
Functional group for esters
-C=O
\
O-C
Functional group for an amine
-NH2
Functional group for a nitrile
-C☰N
1 carbon
Meth-
2 c
Eth-
3 c
Prop-
4 c
But-
9 c
Non-
10 C
Dec-
10 C
Dec-
The stem of each name (hept, e.g) indicates how many. …
Carbons are in the longest chain in one molecule of the compound
The position of side-chains or functional groups is indicated by numbering the carbon atoms in the longest chain. The number starts at the end that produces …?
the lowest possible numbers in the name
What is an alkyl group ? How do you indicate how many alkyl groups?
The number of carbons is in the name e.g. methyl group , ethyl group
A hydrocarbon side-chain.
By di, tri , prop, etc.
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Single covalent bonds are when e.g. carbon forms 4 bonds; is called a….?
Sigma bond
A pair of electrons in a sigma bond is found …?
In a region of space described as a lobe between the nuclei of the 2 atoms sharing the electrons.
What bonds the atoms together in a sigma bond?
The electrostatic attraction between the negatively charged electrons and the two positively charged nuclei.
How many sigma bonds does a carbon atom form?
4
Two carbon-carbon single bonds form what shape and what bond angle ?
A tetrahedral arrangement, 109.5°
A carbon =carbon double bond is made up of what bond (s)? + a more detailed description
Sigma and pi bond.
The carbon atoms will form 3 sigma bonds; an example of sp^2 hybridisation . This leaves each carbon atom with one spare outer electron in a 2p orbital. When these two p orbitals overlap they form a pi bond
What bond shape and angle does a carbon=carbon e.g in ethene
A planar shape.
130°
What are the 3 types of structural isomerism?
- Position isomerism
- Functional group isomerism
- Chain isomerism
There is free rotation in …
C-C single bonds
In position isomerism what stays the same ?
The name of the molecule
In functional group isomerism what 2 things change?
- The name
2. The functional group and therefore they have very different chemical properties
What changes in chain isomerism?
Example of two chain isomers : butane and methylpropane
The thing that differs is the structure of their carbon ‘skeleton’
What are the two types of stereoisomerism?
- Cis-trans isomerism
2. Optical isomerism
There is no free rotation around a ….
Carbon double bond C=C
Cis-trans isomerism is only possible in….and why?
Unsaturated organic compounds , therefore having an C=C double bond .
Why : no free rotation so a different type of isomerism is created.
What is the difference between cis and trans isomerism?
Fact : these compounds will have different physical properties and dome different chemical properties.
💙With Cis both atoms (not c or H) remain fixed on the same side of the C=C double bond.
💙With trans the atoms are positioned across the C=C bond
Definition of chiral centre
A carbon atom with 4 different groups attached,creating the possibility of optical isomers
What is one requirement for an optical isomer?
A chiral centre
How many optical isomers can you form from a chiral centre ?
And give a description of these isomers
2
The two different molecules are mirror images of each other and cannot be superimposed (placed over another like you can’t put your left hand over your right hand)
The effect of 2 optical isomers on polarised light :
Apair of optical isomers will …
Rotate the plane of polarised light by equal amounts but in opposite directions. One will rotate polarised light clockwise and the other anticlockwise.
Organic reactions involve the breaking and making of chemical bonds.
What are the two ways in which covalent bonds can break ?
- Homolytic fission
2. Heterolytic fission
What is homolytic fission?
It is the type of bond breaking in which both atoms involved in the covalent bond leave with one electron from the pair that formed the covalent bond.
The species produced when a bond breaks homolytically are called …..
Free radicals
Free radicals have 2 main characteristics :
HCl ➡ H• + Cl•
- Have an unpaired e- represented by a dot ●
2. Are very reactive
A free radical reaction has three main steps :
- Initiation
- Propagation
- Termination
Description of the initiation step
This step involves the forming of free radicals . This requires an input of energy to break a covalent bond , resulting in two free radicals.
Description of the propagation step
The radicals formed can then attack reactant molecules, generating more free radicals. This step can be thought as a chain reaction, which only stops when free radicals react with each other.
Description of the termination step
2 free radicals reacting together will form a molecule, with no free radicals generated.
What is heterolytic fission?
A type of bond breaking that involves the ‘uneven’ breaking of a covalent bond. The more electronegative atom takes both the electrons in the covalent bond.
How would you show the heterolytic fission of HCl?
H⤵Cl ➡ H^+ + Cl^-
The curly arrow ⤵shoes the movement of the pair of electrons
What causes a carbocation to form ?
When heterolytic fission happens between carbon and an atom which is more electronegative than carbon (e.g. Br).
It takes the pair of electrons and become negative whilst the carbon loses an e- and becomes positive.
There are three types of carbocation, namely:
Where R= an alkyl group
- Primary carbocation (least stable)
H
|
R ➡C +
|
H
- Secondary carbocation
R
⬇
R➡C+
|
H
- Tertiary carbocation (most stable)
R
⬇
R➡C+
⬆
R
Why is the tertiary carbocation the most stable ?
The carbon atom is electron deficient because it only has 3 electrons ( remember it has + charge on it).
Alkyl groups have the effect of spreading out the charge on the carbocation. The more alkyl groups adjacent to the positively charged carbon, the more stable.
Carbocation are an example of a species called….
Electrophiles
Why do alkyl groups ( e.g. -CH3, -C2H5, C3H7, ETC.)have a positive inductive effect on adjacent groups ?
Because of their electron donating nature they tend to ‘push’ electrons away from themselves. Therefore in carbocation the more alkyl groups attached to the positively charged carbon, the less the charge density is on the Carbon atom with the three covalent bonds.
Description of nucleophiles:
Electron rich species , they carry a negative charge , or a partial negative charge.
When a nucleophile donates a pair of electrons, this leads to the formation of a new covalent bond with the electron deficient atom under attack.
An example of an addition reaction
The addition reaction between bromine and an alkene :
C2H4 + Br2 ➡ C2H4Br2 (the double bond breaks)
An example of a dehydration reaction
The dehydration of an alcohol by concentrated sulfuric acid :
(Conc. H2SO4) C2H5OH ➡ C2H4 + H2O
An example of a substitution reaction
The free-radical substitution of alkanes by chlorine in sunlight:
UV light CH4 + Cl2 ➡ CH3Cl + HCl
An example of a substitution reaction
The free-radical substitution of alkanes by chlorine in sunlight:
UV light CH4 + Cl2 ➡ CH3Cl + HCl
An example of hydrolysis
The hydrolysis of a halogenoalkane by water to give an alcohol:
C2H5Br + H2O ➡ C2H5OH + HBr
☆NB ! ☆ hydrolysis with an alkali is faster, and gives slightly different products: An alcohol and another product
C2H5Br + NaOH ➡C2H5OH + NaBr
An example of oxidation
Partial and complete example
Is the partial oxidation of ethanol to ethanal using acidified potassium dichromate (vi) solution :
C2H5OH + [O] ➡ CH3CHO + H2O
Before 1 O and 6 H
After 1 O and 4 H
☆ NB!☆ for the complete oxidation of ethanol to ethanoic acid , using potassium dichromate (vi) solution :
C2H5OH +2 [O] ➡ CH3COOH + H2O
An example of a reduction reaction
The reduction of a ketone, using sodium tetrahydridoborate, NaBH4:
CH3COCH3 + 2[H]➡ CH3CHOHCH3
