Organic nitro compounds comprising dinitro paraffins, nitroalkyl nitrates and nitroalkyl alcohols are prepared by reacting nitrogen tetroxide, in the presence or absence of oxygen, with an aliphatic mono-olefine containing 3-6 carbon atoms or a mixture containing one or more such olefines in the presence of an organic oxygen containing solvent which is at least partly in the liquid phase and treating the reaction products, preferably after removing solvent and oxides of nitrogen, with water or an aliphatic mono-alcohol having less than 6 carbon atoms, said solvent being selected from the following: saturated aliphatic, saturated alicyclic or saturated aliphatic-alicyclic compounds containing carbon, hydrogen and oxygen only and having no oxygen-containing groups except ether or ester groups and no 3- or 4-membered rings, but excluding esters of formic acid; saturated heterocyclic or saturated aliphatic-heterocyclic compounds containing carbon, hydrogen and oxygen only and having only carbon and oxygen in the ring and no other groups except hydrogen, hydrocarbon, ether or ester groups, but excluding such compounds containing 3- or 4-membered rings. Preferably, these solvents at atmospheric pressure boil below 180 DEG C., and melt below 50 DEG C. They may be used in admixture with other inert solvents, for example, saturated hydrocarbons. Suitable solvents of the specified type are alkyl mono-ethers such as methylated ether, di-isopropyl ether, di-isoamyl ether, di-n-propyl ether, di-n-amyl ether; diethers, such as methylal; dioxan, tetrahydrofuran, tetrahydropyran, methyl tetrahydropyran; esters of saturated aliphatic monocarboxylic acids such as ethyl acetate, propyl acetate and amyl acetate. The nitration is preferably carried out in the presence of oxygen, air or a mixture of oxygen with an inert gas or gases, generally using from about 0.1 to about 0.3 mol. of oxygen per mol. of hydrocarbon reactant. Reaction conditions must be such that the organic solvent is at least partly, and preferably mainly, in the liquid phase; low temperatures are favoured especially below the liquefaction temperature of nitrogen tetroxide. A mixture of mono-olefines or a mixture containing mono-olefines may be employed, but preferably single pure hydrocarbons are used. With C3 and C4 olefines it is preferred to pass the olefine in gaseous form into a solution of nitrogen tetroxide in the selected type of solvent, generally using an excess of the nitrogen tetroxide; with C5 and C6 olefines, the olefine is preferably dissolved in the solvent and the nitrogen tetroxide added in the liquid form or as a solution in the solvent, using an amount of nitrogen tetroxide equivalent to the olefine. Preferably, a high ratio of N2O4 to solvent is employed, for example 0.5-0.9 mol. of N2O4 per mol. of mono-ether. The treatment of the resulting reaction mixture with water or an alcohol referred to above is necessary in order to hydrolyse unstable alkyl nitrites formed in the reaction to the nitro-alkyl alcohols. Generally, water is used, since when the nitro alcohols are water soluble they may be extracted by the water from which phase they can be isolated by solvent extraction, for example, with methylated ether followed by vacuum distillation; the dinitro - paraffins and nitro-alkyl nitrates when solids are then recovered from the residue by freezing out from an organic solvent, for example, a lower aliphatic mono-alcohol or otherwise recovered by fractional distillation. When hydrolysis is effected with an alcohol, the three nitro compounds are obtained as a solution in the alcohol from which the dinitro compound may be recovered by freezing out. Other methods of recovery may be employed. Thus, the dinitro paraffin may be isolated by freezing out from the main reaction product before the hydrolysis step and before or after removal of solvent and excess nitrogen tetroxide. Again, if in the main reaction a solvent boiling below 100 DEG C. is used, then water may be added to the product, the solvent removed by vacuum distillation, the aqueous layer containing the nitro alcohols separated and the nitro alcohols recovered by solvent extraction followed by fractional distillation while the dinitro paraffins and nitro-alkyl nitrates are recovered from the residual oil by freezing out from a solvent or by fractional distillation. Alternatively, a water-immiscible solvent may be used in the main reaction, the products then being treated with water and the aqueous layer separated from the solvent layer and the products recovered as described in the preceding modification. A maximum yield of nitro-alkyl alcohols is obtained by using no oxygen or only up to about 0.15 mol. of oxygen per mol. of olefine; best yields of nitro-alkyl nitrates are obtained using from 0.25 mol. and upwards of oxygen per mol. of olefine and excess nitrogen tetroxide, and no water should be present. In examples: (1) propylene was passed into a solution of N2O4 in dry methylated ether at 0 DEG C. and the reaction product washed with water after removal of solvent and excess N2O4; the aqueous portion was ether extracted and nitro propanol recovered from the extract by distillation; the water-insoluble residue was distilled under reduced pressure yielding 1,2-dinitropropane; (2) a mixture of propylene and oxygen was reacted and the products worked up as in (1) above, there being recovered 1-nitro-propanol-2 and a mixture of 1,2-dinitropropane and the nitrate ester of 1-nitro-propanol-2; (3) the solvent employed in (1) above was replaced by methylal; (4) isobutene was passed into a solution of N2O4 in dry methylated ether; the product was washed four times with water after removal of solvent and excess N2O4, the emulsions formed in the later washing being broken by addition of a wetting agent known under the Registered Trade Mark "Calsolene"; ether extraction of the combined aqueous portions followed by distillation yielded nitro-tertiary butanol; the water - insoluble residue was dissolved in methanol and 1,2-dinitroisobutane frozen out by cooling; after removing methanol from the mother liquor followed by fractional distillation, more dinitroisobutane together with nitro-tertiary butyl nitrate was recovered; (5) and (6) the solvent employed in (4) was replaced by dioxan and ethyl acetate respectively; (7) gaseous isobutene together with oxygen was passed into an ethereal solution of N2O4 and nitro - tertiary butanol, nitro - tertiary butyl nitrate and 1,2-dinitroisobutane recovered from the products as in (1) above; (8) isobutene was reacted with a methylal solution of N2O4 and after the water treatment there were recovered as in (4) above, nitro-tertiary butanol and 1,2-dinitrobutane; (9) and (10) butene-2 and butene-1 were treated as in (1) above to yield 2-nitro-butanol-3 and 2,3-dinitrobutane and 1-nitro-butanol-2 and 1,2-dinitrobutane respectively. It is stated also that butene-2 gives rise to 2-nitro-butanol-3 nitrate and butene-1 to 1-nitro-butanol-2 nitrate. The following products are believed to be new compounds: 1,2-dinitropropane characterised by formation of 1,2-diamino propane on reduction and preparation of its hydrochloride and dipicrate; 1-nitro-2-propanol nitrate yielding 1-amino-2-propanol on reduction; 1,2 - dinitrobutane characterised by formation of 1,2-diaminobutane on reduction and preparation of its hydrochloride and dipicrate; and nitro-tertiary butyl nitrate.