These often are not given a particular shape name, but never-the-less, an appreciation of the 3D spatial arrangement is expected e.g.

Ethane consists of two joined 'tetrahedral halves', in which all C-C-H and H-C-H bond angles of 109^o.

ball and stick model of ethane

space-filling model

Benzene is a completely planar molecule, with all C-C-C or C-C-H bond angles of 120^o.

Shapes and bond angles of organic molecules

Most bond angles in organic chemistry can be accurately or approximately predicted using bond repulsion theory (with some notable exceptions at the end).

Two groups of bonding electrons around the 'middle' atom of the bond give an angle of 180^o.

Alkynes have a single bond pair and a triple bond pair around the middle carbon.

e.g. the R-C-C angle in R-CC-R alkynes, ethyne H-CC-H has linear shape

Dienes with adjacent double bonds have two double bond pairs around the 'middle' atom.

e.g. the C-C-C angle in >C=C=C<

e.g. in propa-1,2-diene CH₂=C=CH₂, and buta-1,2-diene CH₂=C=CH-CH₃

Diazonium salts e.g. the C-NN: bond in diazonium cations like [C₆H₅-NN:]⁺ 

Three groups of electrons around the 'middle' atom of the bond give an angle of 120^o.

Two single bond pairs and double bond pairs.

The H-C-H, C-C-H angles associated with the alkene group >C=C< which leads to a planar shape for ethene itself.

The angles associated with the carbonyl group >C=O e.g. (i) H-C=O, C-C=O in aldehydes, ketones and carboxylic acids and derivatives and (ii) C-C(=O)-O, C-C(=O)-C  in carboxylic acids and their derivatives.

(i) RCHO, RCOR and (ii) RCOOH, RCOOR, RCOCl, RCONH₂ etc.

Two 'averaged 1.5' bonds of the delocalised benzene ring and a single bond pair of the bond attaching an atom to the ring.

e.g. in benzene itself, all the -C-C-C- or -C-C-H bonds are 120^o and is a completely planar molecule.

and in benzene derivatives C-C-X where X might be Cl, N (from NO₂ or NH₂), O (from phenol -OH or ether -OR) etc.

A single bond pair, double bond pairs and a lone pair (e.g. on the N atom, x-ref ammonia).

In diazo compounds R-N=N-R, the R-N=N bond angle is 120⁰.

Four groups of electrons around the 'middle' atom of the bond usually gives an angle of about 109^o. The orbitals would point to the corners of a tetrahedron.

Four single bond pairs give all the C-C-C or H-C-H or C-C-H angles in most (see below) saturated systems e.g. alkanes, chloroalkanes etc..

Also the R-N-R angle in the quaternary ammonium salt ion [NR₄]⁺.

Three single bond pairs and a lone pair (x-ref ammonia above).

e.g. the H-N-H, C-N-H bond angles in amines R-NH₂, R-NH-R, :NR₃ etc.

Two single bond pairs and two non-bonding lone pairs (x-ref water above).

e.g. the C-O-H angle in alcohols and phenols and the >C-O-C< angle in ethers and esters

Some significant exceptions to the above general rules.

Despite the four single bond pairs, the C-C-C bond angle in cyclopropane is a 'forced' 60^o. and the H-C-H angle is over 109⁰, from a distorted 'tetrahedral' situation.

Despite the four single bond pairs, the C-C-C bond angle in cyclobutane is on face value a forced 90^o and the H-C-H angle is over 109⁰. However there is evidence to suggest it oscillates between two bent conformers with an 'average' bond angle of ~109^o.

For cyclopentane onwards, the ring is 'puckered' with C-C-C, C-C-H and H-C-H bond angles of ~109^o.

EXAMPLES analysed and summarised for you ...

but I suggest you sketch some out and mark on all the angles, see the end 'scribbles'

methanol all H-C-H, C-O-H and H-C-O angles ~109^o

chloromethane all H-C-H and H-C-Cl angles ~109^o tetrahedral shape

propane all H-C-H, C-C-H or C-C-C angles are 109^o 

ethene

all H-C-H or H-C=C angles are 120^o in the completely planar molecule of ethene

propene H-C-H 109^o in the CH₃- group, but the

H-C=C, C-C=C, C=C-H and =CH₂ angles are 120^o

propyne the H-CC and CC-C angles are 180^o

and the C-C-H and H-C-H in -CH₃ are 109^o linear molecule shape

methylbenzene C-C-C in ring 120^o and C-C-C(H₃) off the ring 120^o

but the C-C-H of the C-CH₃ and the H-C-H in the -CH₃ off the ring are 109^o 

bromoethaneall H-C-H, H-C-C, C-C-Br, H-C-Br angles are 109^o 

ethanolall H-C-H, H-C-C, C-C-O, H-C-O, C-O-H angles are 109^o 

methoxymethaneall H-C-H, H-C-O, C-O-C angles are all 109^o 

phenolC-C-C in ring 120, C-C-H of ring 120^o and C-O-H off ring is 109^o 

ethylamine all H-C-H, C-C-H, C-C-N and C-N-H angles are all 109^o 

butanone H-C-C, H-C-H and (O=)C-C-C on right are all 109^o 

and C-C=O on left, C-C(=O)-C and O=C-C on right are 120^o 

methanoic acidH-C=O, H-C-O(-H) and O=C-O are 120^o and C-O-H is 109^o 

ethanamide   H-C-H, H-C-C, H-N-H and C-N-H are all 109^o 

and C-C=O, C-C-N and O=C-N are 120^o 

ethyl ethanoate   all H-C-H, O-C-C (right), H-C-C (left)

and C-C-H (right) are all 109^o, and C-C=O, C-C-O (left) and O=C-O are 120^o 

ethanoyl chloride   H-C-H and H-C-C are 109^o 

and C-C=O, C-C-Cl and O=C-Cl are all 120^o 

diazo dye all the C-C-C, C-C-H, C-N=N, C-C-N(=) bond angles

of/off the ring are all 120^o but the C-O-H of the phenol group on the right is 109^o.

the SCRIBBLES!

which will eventually be replaced by neater diagrams!

SEE ALSO Appendix 1-4 on separate page: The shapes, with ox diagrams and bond angles, of some other molecules/ions of carbon, nitrogen, sulphur and chlorine besides those on this page and again the 'scribbles' will be replaced by neat diagrams eventually!

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