H3 Chemistry 9813 · Study focus: H3 Chemistry: Use Newman and other stereochemical projections
H3 Chemistry: Use Newman and other stereochemical projections
Start from the governing chemical model, test it against evidence, then transfer the reasoning to an unfamiliar case.
Your success criteria
- Use Newman and other stereochemical projections
- Use named chemical evidence.
- Transfer the governing reason to an unfamiliar case.
Choose a sight line
A Newman projection is a view directly along one specified carbon–carbon bond.
Fix the viewing direction before assigning any substituent to the front or rear carbon.
Projection conventions
The front carbon is a point with three bonds; the rear carbon is a circle with bonds beginning at its rim.
Staggered bonds are offset by 60°, whereas eclipsed front and rear bonds align at 0°.
Copy the three substituents belonging to each viewed carbon before arranging their angular positions.
Changing a dihedral angle changes conformation; rotating the complete drawing on paper does not.
Text alternative: Text identifies sight line, atom ownership, bond offset and named dihedral without relying on colour.
Preserve structure in two dimensions
Copy the three substituents belonging to each viewed carbon before arranging their angular positions.
Changing a dihedral angle changes conformation; rotating the complete drawing on paper does not.
Build anti-butane
View butane from C2 towards C3, so C2 is the point and C3 the circle.
Place one methyl on each carbon 180° apart and offset all rear bonds to obtain staggered anti-butane.
- Draw anti-butane viewed C2→C3.
Open the feedback checkpoint after attempting
- Award front/rear ownership, staggered bonds and a 180° methyl–methyl dihedral.
Control a gauche drawing
Keep butane connectivity fixed while rotating only the rear carbon relative to the front.
A 60° methyl–methyl separation in a staggered projection is gauche.
- Convert the anti drawing into gauche without relabelling atoms.
Open the feedback checkpoint after attempting
- Rotate one carbon 120° relative to the other so the named methyl dihedral becomes 60°.
Transfer to a haloalkane
For 1-bromo-2-chloroethane viewed C1→C2, Br belongs to the front carbon and Cl to the rear.
State the requested Br–C–C–Cl angle rather than relying on top or bottom placement.
- Draw a staggered conformer with Br anti to Cl.
Open the feedback checkpoint after attempting
- Show Br and Cl on different viewed carbons, separated by 180°.
Do not move substituents between carbons
Projection changes never alter which atoms are bonded.
A rear bond starts at the circle rim; it does not start at the central point and pass through the circle.
- Repair: ‘Both methyl groups may be placed on the front carbon to make anti-butane.’
Open the feedback checkpoint after attempting
- Reject it because butane has one methyl substituent on each of C2 and C3.
Audit the representation
Check sight line, ownership, connectivity, offset and named dihedral in that order.
Fischer projections are explicitly not required for this syllabus outcome.
- State four checks for a valid Newman drawing.
Open the feedback checkpoint after attempting
- Name the sight line, front/rear substituents, unchanged connectivity and requested dihedral.