Fundamentals of organic chemisty Flashcards
What is the fundamental element of organic chemistry?
- Carbon because it can form up to four bonds
- Carbon is abundant
- Organic substances can be synthesized from inorganic substances e.g. urea
What is a homologous series?
- A series of closely related compounds in a family
- Members of the same homologous series have:
the same general formula, same functional group, differ by a CH2 group, have similar properties, increasing physical properties (e.g. boiling point)
What are the characteristics of the alkanes?
- They are hydrocarbons and are used as fuels. They react with oxygen to produce carbon dioxide and water
- The successive members differ by a CH2 group
- The melting and boiling point increases when the number of carbons and molecular mass do too
What does the boiling point and melting point of alkanes increase?
- When the molar mass increases, the strength of the intermolecular forces increase too, hence higher melting and boiling point
- They become increasingly solid and start off as gases
What is catenation?
- Being able to form covalent bonds with itself, which results in long chains and rings of carbon
- This gives rise to millions of carbon-containing compound
What is the empirical and molecular formulae?
- Empirical formula represents the simplest whole-number ration of atoms
- Some alkanes have the same empirical and molecular formula
- The molecular formula represents the actual number of each type of atom in a compound
Into what 3 sections can the structural formula be divided into?
- It can be divided into full structural formulae, condensed structural formula and skeletal formulae
What is the full structural formulae?
- All atoms and the bonds between them are shown (a single line represents a single covalent bond)
What is the condensed structural formulae?
- The bonds between the atoms are omitted e.g. CH3CH2CH3
What is the skeletal formulae?
- All atoms are omitted leaving only the backbone of the molecule
- The carbons are at the intersection of each line and at the end of the line
- Hydrogen atoms are not shown at all, the number is assumed based on the valency of carbon (4 bonds)
- The functional group is shown
How does a 3D formulae structure look like?
- Bond angles are 90° and 180° bond angles
- This does not represent the actual molecular geometry of the molecule
- Some molecules are shown in a stereochemical formula, which is drawn on paper and looks 3 dimensional
Check book
What are branched and cyclic structures?
- Alkanes are unbranched but are not perfectly straight due to the 109.5° angles. But this is referred to straight chain structures
- Other structures such as 2,2,4-trimethylpentane is a branched-chain alkane (has methyl groups at certain positions)
- Cyclic alkanes are represented by polygons. The corners of the polygon represent a carbon atom together with the hydrogen atoms bonded to it
Check book
What are structural isomers? What is it divided into?
- Compounds that have the same molecular formula but a different structural formula (different arrangements of atoms)
- Structural isomerism is divided into: chain isomerism, position isomerism and functional group isomerism
What are chain isomers?
- The isomers are usually branched and a group (methyl group) is often added
- These are chain isomers, the chemical properties are quite similar but have different physical properties
- The more carbon atoms there are, the greater the number of possible isomers
- Branched isomers have lower boiling points than straight-chain isomers
What is position isomerism?
- When the functional group is attached in different positions
- This usually happens when there is a double bond present (alkenes) which can exist in different positions
- This also applies to alcohols that have a hydroxyl group (OH)
- The placement is given by the number in the name e.g. butan-1-ol has the OH group on the first carbon, butan-2-ol has the OH on the second carbon
What is functional group isomerism?
- The isomers have the same molecular formula but different functional groups
- E.g. propanal (-COH) and propanone (-CO) functional groups
- Another example are propanoic acid and methyl ethanoate which have the same molecular formula but different functional groups
Check book
What are functional groups?
- Single atoms or groups of atoms that give organic compounds their characteristic properties
- They are the reactive part of the molecule
Table in book
Give the functional group and general formula of alkanes.
- Alkyl group CH2-CH2
- CnH2n+2
Give the functional group and general formula of alkenes.
- Alkenyl CH=CH
- CnH2n
Give the functional group and general formula of alkynes.
- Alkynyl -C≡C-
- CnH2n-2
Give the functional group and general formula of halogenoalkanes.
- R-X
- CnH2n+1X
X is the halogen
Give the functional group and general formula of alcohols.
- Hydroxyl R-OH
- CnH2n+1OH
Give the functional group and general formula of aldehydes.
- Carbonyl R-CHO
- CnH2n+1CHO
- Be aware of the C=O double bond
Give the functional group and general formula of ketones.
- Carbonyl R-CO-R’
- CnH2n+1COCxH2x+1
Give the functional group and general formula of carboxylic acids.
- Carboxyl R-COOH or R-CO2H
- CnH2n+1COOH
What do the R and R’ stand for in functional groups?
- They represent hydrocarbon chains (alkyl groups) they can be identical or different
Give the functional group and general formula of ethers.
- R-O-R’ ether
- CnH2n+1OCmH2m+1
Give the functional group and general formula of esters.
- Ester R-COO-R’
- CnH2n+1CO2CmH2m+1
Give the functional group and general formula of amines.
- Amine or amino R-NH2
- CnH2n+1nH2
Give the functional group and general formula of amides.
- Carboxamide or amido R-CONH2
- CnH2n+1CONH2
Give the functional group and general formula of nitriles.
- R-CN nitrile (tripple bond)
- CnH2n+1CN
Give the functional group and general formula of arenes.
- Phenyl
- C6H5 (benzene ring)
How can functional groups be classified?
- As acidic or basic, depending on their ability to donate or accept a proton
- They will act as either Brønsted–Lowry acids or Brønsted–Lowry bases
- Carboxyl group act as acids (donate a proton) and forms carboxylate ion (R-COO-)
- Amine group act as bases (accept proton)
What is the IUPAC nomenclature?
Universal system of naming organic compounds by taking these factors into consideration:
- Stem that depends on the no. of carbon atoms in the longest chain
- Suffix (end) differs according to the functional group
- Prefix (start) to identify the position of substituent groups
What are the stems used for naming compounds relating to the number of carbon atoms in the longest chain?
1- meth 2- eth 3- prop 4- but 5- pent 6- hex
How do you name branched-chain alkanes?
- Identify longest carbon chain (gives stem) e.g. pentane
- Identify the side-chains (gives the prefix. If there is more than one side chain of the same type, the prefixes are di, tri, tetra, etc. If there are multiple different side chains, must be listed in alphabetical order
e. g. 2,3-dimethyl - The position of the side-chain (no. of carbon) must be written in the name
e. g. 2,3-dimethylpentane
Name the alkyl groups.
methyl, ethyl, propyl, butyl
These are the side chains (R-gorups)
How do you name alkenes?
- The suffix is ene and a number is written inside the compound to show the position of the C=C double bond (if the compound has 4 or more carbon atoms)
e. g. pent-2-ene - The lowest number is assigned (count from shortest side)
How do you name alkynes?
- Named using the stems followed by the suffix -yne
- The number in the same shows the position of the carbon triple bond
- e.g. but-1-yne
How do you name alcohols?
- Using stem and suffix -anol
- Branched-chain alcohols are named in a similar way to branched-chain alkanes as the side-chain is assigned a number and prefix
- e.g. 2-methylpropan-1-ol
- Alcohols contain two diols (hydroxyl functional group) and their position is indicated by numbers e.g. ethane -1,2-diol
What are the primary, secondary and tertiary alcohols?
- Number of Carbon atoms bonded to other Carbon atoms bonded to functional group
Check book
How do you name carboxylic acids?
- Using stem and suffix -anoic acid
- Contain functional group COOH (containing on double bond)
- Carboxylic acids with two functional groups have a suffix of -dioic
e. g. ethanedioic acid
How do you name aldehydes and ketones?
- Aldehydes: using the stem and suffix -anal
e. g. methanal (HCHO) - Ketones: using the stem and suffix -anone
- The first ketone is propanone
- The position of the carbonyl group (C=O) is indicated by the number
e. g. pentane-2-one
Why do ethers not form hydrogen bonds and what properties do their have?
- They are composed out of two alkyl groups bonded by an oxygen atom and they lack the ability to form hydrogen bonds between molecules
- This is because they lack an oxygen atom directly bonded to a hydrogen atom
- They are volatile (easily evaporate)
- Ethers cannot mix with water
how do you name ethers?
- The shorter alkyl group (CH2) had a prefix alkoxy (meth, etc. contain corresponding number of carbons) and the longer alkyl group is named after the alkane
- A number is used to signify to which carbon atom the alkoxy group is bonded to
- The two alkoxy are bonded by an O
How do you name nitriles?
- Nitriles have a functional group (nitrile group) C≡N
- The carbon atom of the nitrile group counts as the first atom of the chain, the suffix -nitrile is added
How do you name amines? On what basis are they classified?
- Contain functional group (amine group) -NH2
- They are classified as primary, secondary or tertiary, this depends on how many alkyl groups are bonded to the nitrogen atom of the amine group
- Suffix -amine
- There are alternative naming systems of amines (data booklet)
How are primary and secondary amines named?
- Primary named using stem and suffix -amine
- Secondary named on the basis of the longest unbranched carbon chain bonded to the nitrogen atom of the amine group
- The second alkyl group is named using prefix methyl, ethyl, etc. with an N. The NH group separates the longest unbranched carbon chain and the second alkyl group
How are tertiary amines named?
- They contain three alkyl groups bonded to the nitrogen atom of the amine group
- Names using the prefix methyl-, ethyl-, etc. and then named after the longest unbranched carbon chain and end with -amine
- An N is in front of the name (which determines the position and number of the alkyl groups)
How are amides related to carboxylic acids?
- In the place where carboxylic acids have the -OH group, the NH2 group replaces it and the suffix changes to -amide
- The carbon in the functional groups counts to the longest carbon chain
On what do the physical properties depend on?
- Depend on intermolecular forces (London dispersion forces, dipole-dipole and hydrogen bonding)
- Hydrogen are strongest which are between carboxylic acids and alcohols hence have high boiling points
What factors effect the volatility of an organic compound?
- Volatility (how easily something evaporates)
Depends on: - Molar mass, boiling point, intermolecular forces
- Isomers; branched or straight
- Nature of functional group
Explain how the molar mass, boiling point and intermolecular forces effect the volatility.
- The boiling point increases when the molar mass increases, which means the London dispersion forces become stronger between the molecules
- More energy is required to break them and change the physical state
- Early members of alkanes are gases and liquids at r.t.p the later are solids
- Boiling point increases down a homologous group
Explain how the structure of isomers effect the volatility.
- Branched-chain isomers have a lower boiling point than straight chain isomers
- A branched-chain is in a spherical shape which results in less surface contact with the molecules than with straight-chain isomers. They have weaker intermolecular forces and lower boiling points
Explain the effect of the nature of the functional group on volatility.
- Polar functional groups result in stronger dipole-dipole interactions between the molecules and therefore higher boiling points
- Functional groups that contain OH or NH bonds, have hydrogen bonds between them, high boiling point
- Ethers for example have no hydrogen bonds and therefore evaporate at lower temperatures than alcohols with similar molar masses
Which intermolecular forces are involved in which functional groups?
London dispersion forces - C-C (alkane) - C-X (halogenoalkane) Dipole-dipole interactions - R-CHO (aldehyde) - CO (Ketone) - R-NH2 (amine) Hydrogen bonding - R-OH (alcohol) - R-COOH (carboxylic acid) Highest boiling point
What other factor needs to be compared regarding the boiling points?
- The molar mass (different number of carbon atoms)
- When a hydrogen bond is formed between two molecules, this results in an increased boiling point because the increased molar mass of the combined molecules and London dispersion forces
What effects the solubility in organic compounds?
- Depends on the ability to form hydrogen bonds with water molecules
- Molecules that can easily form those bonds, are soluble
- The non-polar hydrocarbon part of a molecule may interfere with this ability
- When the number of carbons increase (length of hydrophobic hydrocarbon chain) decreases the solubility in water because the hydrophobic character increases
- Non-polar molecules are usually insoluble as they cannot form hydrogen bonds
What is the hydrophobic character?
- The non-polar hydrocarbon chain of a molecules which is insoluble in polar solvents such as water
- This reduces the solubility of the substance
Which organic compounds can be classified?
- Alcohols, halogenoalkanes and amines
On what basis are alcohols and halogenoalkanes classified into primary, secondary of tertiary structures?
- Depends on the number of carbon atoms bonded to the carbon atom that is directly linked to the functional group
- Check book for examples of alcohols and halogenoalkanes
On what basis are amines classified into primary, secondary of tertiary structures?
- Depends on the number of alkyl groups that are bonded to the nitrogen atom of the amine group
- The CH2 group next to the N counts as an alkyl group too
- Check book for examples
What are aromatic hydrocarbons?
- A.k.a arenes
- These aromatic compounds release vapour (that can be smelled)
- They contain a benzene ring which is called pheny functional group
- Formula of benzene: C6H6
What is benzene resonance structure called?
- The resonance structures known as Kekulé structures, theory that it has six carbons, was accepted for many years
What 2 pieces of evidence disprove the Kekulé resonance structure of benzene?
- All carbon-carbon bond lengths in benzene are identical, 140 picometers (pm)
- Only one isomer exists for 1,2-disubstituted benzene compounds
Explain the first piece of evidence for the resonance structure of benzene.
- In benzene there are alternating single and double bonds, single (154pm) and double (134pm). But the length of them is 140pm, hence the bonds are neither single nor double bonds but intermediate in length
- The bond strengths in benzene are also identical, intermediate between single and double bond
Physical evidence
Explain the second piece of evidence for the resonance structure of benzene.
- There is only one structure of benzene with disubstitued chlorine. Only one isomer exists for 1,2-disubstituted benzene compounds
- Benzene contains alternating single and double bonds, hence there should be two isomers such as 1,2-dichlorobenzene
- Only one isomer of 1,2-dicholorbenzene exists, which proves that benzene does not have double bonds
What is the actual structure of benzene?
- Each carbon is bonded to 2 other and 1 hydrogen atom. Each carbon only uses 3 of its bonds
- The remaining electrons are delocalised and shared between more than two nuclei
- Benzene undergoes electrophilic substitution (chemical evidence)
Explain the role and position of the delocalised electrons.
- The delocalised electrons are represented by a circle in the middle of the hexagon-shaped structure
- They are called pi (π) electron cloud which refers to the type of bonding
Where else is the benzene structure used?
- In aromatic compounds that contain a phenyl functional group
- It is unsaturated (contains double bonds)
