Define the term nucleophile.

A species with a lone pair of electrons that it donates to an electron-deficient atom to form a covalent bond.

Why is the carbon atom of a carbonyl group electron-deficient?

Oxygen is considerably more electronegative than carbon, so it draws the shared electrons towards itself and leaves the carbon short of electron density.

Write the partial charges on a carbonyl group.

The group is polarised as Cδ⁺=Oδ⁻.

Which atom of the cyanide ion attacks the carbonyl carbon?

The carbon atom of the cyanide ion, which carries the lone pair and the negative charge.

Describe the curly arrows in the first step of the mechanism.

One curly arrow runs from the lone pair on the carbon of CN⁻ to the carbonyl carbon, and a second runs from the C=O π bond onto the oxygen atom.

Why must the second curly arrow be drawn in that first step?

Carbon can form only four bonds, so as the new carbon–carbon bond forms the π bond must break, its pair of electrons moving onto the oxygen.

OCR A-Level Chemistry B H433

Development of Practical Skills in Chemistry

Topic overview Planning experiments Implementing: apparatus, units and recording data Significant figures and titration calculations Graphs, gradients and drawing a conclusion Anomalous results, precision, accuracy and types of error Calculating uncertainties and improving a method Hazards, risk and control measures Recording, processing and judging data Measuring pH, mass and volume, and choosing an indicator Reflux, distillation, purification and the standard tests PAG1 to PAG6: moles, enthalpy, qualitative analysis and organic synthesis PAG7 to PAG12: electrochemistry, rates and pH

Elements of Life

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Topic overview Molar gas volume and the ideal gas equation Gas volume calculations and measuring a gas in the laboratory Bonding and shape in organic molecules Enthalpy changes: definitions and standard conditions Bond enthalpies q = mcΔT and measuring an enthalpy change in solution Burning a fuel, correcting for heat loss, and the assumptions made Hess' law and enthalpy cycles Catalysts, heterogeneous catalysis and catalyst poisons Cracking and how it is carried out The pollutants from burning fuels and their effects Catalytic converters and cutting emissions Aliphatic and aromatic compounds, functional groups and general formulae Deducing formulae and naming a branched compound Combustion of organic compounds Addition of bromine and hydrogen halides, and the test for unsaturation Hydrogenation and hydration of alkenes Addition polymerisation Electrophilic addition mechanism Displayed, shortened and skeletal formulae Chain, position and functional group isomerism Why alkenes show stereoisomerism, and the E/Z and cis/trans rules Naming and comparing the stereoisomers Sustainable fuels: benefits and risks

Elements From the Sea

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The Ozone Story

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Oceans

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Developing Metals

Topic overview Manganate(VII) titrations and their calculations Thiosulfate titrations, recording results and good technique Shapes of complexes and coordination number Balancing redox equations involving acid-base reactions Simple electrochemical cells Action of an electrochemical cell Standard electrode potentials and calculating E°cell Rusting and how it is prevented Transition metals: definition, oxidation states and colours d-block electron configurations of the atoms and their ions Why transition metals show variable oxidation states Ligands and complex ions Coordinate bonding and what makes a ligand Bidentate and multidentate ligands, and finding a complex's formula Reactions of Fe2+, Fe3+ and Cu2+ with hydroxide and ammonia Catalytic activity of transition metals Origin of colour in transition metal complexes Colorimetry

Colour by Design

Topic overview How dyes attach to fibres Structure of a dye molecule Fats and oils Arenes and delocalisation Representations of benzene and enthalpy of hydrogenation Tests for the common functional groups Identifying a polyfunctional molecule from a set of test results Halogenation and nitration of benzene and the electrophiles involved The nitration mechanism, sulfonation and the Friedel-Crafts reactions Diazotisation and why it is done cold Coupling reactions, azo dyes and the route from benzene Oxidising an aldehyde and the three carbonyl tests Cyanohydrin formation and its use in synthesis Using the Data Sheet reactions to plan a route Choosing between routes on yield and atom economy Nucleophilic addition mechanism Classifying organic reactions and unfamiliar mechanisms Origins of colour in organic molecules How gas-liquid chromatography separates a mixture Retention time, peak area and the limits of the technique

Chemical Literacy

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Mathematical Skills in Chemistry

Topic overview Units, standard form and the mole in calculations Yield, atom economy and logarithmic quantities Significant figures, means and handling data Symbols, and rearranging the standard equations Substituting into rearranged equations Reading spectra and kinetics graphs Gradients, calibration lines and the Arrhenius plot Shapes and bond angles from electron pair repulsion Chiral centres, E/Z isomerism and optical activity

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Nucleophilic addition mechanism

3 things to know
Components 01, 02 and 03

Overview

Recall questions on why the carbonyl carbon is electron-deficient, the partial charges, the curly arrows, and why the reaction is nucleophilic addition.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Numbers

What is a nucleophile, why is the carbonyl carbon electron-deficient, and what partial charges does the group carry?

Numbers

What does ethanal give with hydrogen cyanide, and why is the reaction classed as nucleophilic addition?

Process

Where must a curly arrow begin, why does cyanide addition to an unsymmetrical carbonyl give two optical isomers, and how do alkenes and carbonyl compounds differ in how their additions start?

Questions from this subtopic

Each one with the model answer underneath.

1
Define the term nucleophile.
Model answer
A species with a lone pair of electrons that it donates to an electron-deficient atom to form a covalent bond.
2
Why is the carbon atom of a carbonyl group electron-deficient?
Model answer
Oxygen is considerably more electronegative than carbon, so it draws the shared electrons towards itself and leaves the carbon short of electron density.
3
Write the partial charges on a carbonyl group.
Model answer
The group is polarised as Cδ⁺=Oδ⁻.
4
Which atom of the cyanide ion attacks the carbonyl carbon?
Model answer
The carbon atom of the cyanide ion, which carries the lone pair and the negative charge.
5
Describe the curly arrows in the first step of the mechanism.
Model answer
One curly arrow runs from the lone pair on the carbon of CN⁻ to the carbonyl carbon, and a second runs from the C=O π bond onto the oxygen atom.
6
Why must the second curly arrow be drawn in that first step?
Model answer
Carbon can form only four bonds, so as the new carbon–carbon bond forms the π bond must break, its pair of electrons moving onto the oxygen.

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