Übersetzung für "Sterische hinderung" in Englisch

The steric hindrance by reporter molecules can reduce the yield and efficiency of oligonucleotide syntheses.

The steric hindrance is eliminated due to the cleavage of the radical from the photoinitiator.

These include inorganic bases and organic bases which are difficult to acylate, for example due to steric hindrance.

Said polyisocyanates are compounds in which, if possible, the NCO groups participating in the reaction are not at all sterically hindered.

This is presumably due to steric hindrance by the triphenyl phosphane ligands which prevent transfer of hydride.

In some embodiments, secondary and tertiary amines and phosphines are selected as catalysts because of steric hindrance of the active center.

It must be taken into account here, however, that there must not be any steric hindrance of the two parts attached by fusion.

The reactions involved are the substitution reactions customary for secondary amines, although, because of the steric hindrance resulting from the methyl group or the group --CH2 --R21, these reactions proceed more slowly.

Most suitable are those ketones that facilitate removal from the system of the water of reaction, and the substituents of which effect the least possible steric hindrance.

This is presumably due to the fact that in spite of their high content of active hydrogen atoms, they are only very slowly built into the polyurethane during the foaming process because of steric hindrance.

Suitable bases include, for example tertiary aliphatic and aromatic amines such as pyridine or triethylamine, or sterically hindered, difficultly acylatable secondary amines, such as dicyclohexylamine,

If the carboxyl group formed in the first stage of the reaction is not prevented, for example by steric hindrance, from undergoing further reaction, the second reaction stage of the process according to the invention gives rise to compounds containing excess isocyanate groups, sulfonic acid alkyl ester groups and amide groups.

In order to facilitate ketimine formation, preference is given to those ketones which permit the water of reaction to be removed from the system in a simple manner and in which the substituents exert the least possible steric hindrance effect.

The alkyl-substituted aromatic polyamines having molecular weights of up to 500, preferably of from 122 to 400, are expediently primary aromatic diamines which contain, in the ortho-position to the amino groups, one or more alkyl substituent which reduces the reactivity of the amino group through steric hindrance, are liquid at room temperature and are at least partially, but preferably fully miscible with the polyazomethine-containing polyoxyalkylene-polyamine mixtures (b) under the processing conditions.

It is assumed that the steric hindrance of the axially configured aminomethyl group at the C3 atom leads to this reduction of the reactivity.

The alkyl-substituted aromatic polyamines, having molecular weights of up to 500, preferably from 122 to 400, are in particular primary aromatic diamines which contain, in the ortho-position to the amino groups, at least one alkyl substituent which reduces the reactivity of the amino group due to steric hindrance, and which are liquid at room temperature and are at least partially miscible, but preferably infinitely miscible, under the processing conditions with the N-proxylated polyoxyalkylene-polyamines (b) or the mixtures of N-propoxylated polyoxyalkylene-polyamines (b) and polyoxyalkylene-polyamines containing primary amino groups (bi).

It is assumed that the antibody hereby reduces the affinity of the enzyme substrate for the active part of the enzyme either by steric hindrance or by a conformation change of the enzyme or by preventing the conformation change necessary for the catalytic activity of the enzyme.

Preferably, these are cyclic amines, in particular derivatives of 5-membered, 6-membered or 7-membered heterocyclic ring systems with 1 or 2N atoms which ring systems have tertiary C atoms in both ortho-positions relative to the N atom, whereby steric hindrance of the N atom is effected.

For example, N,N'-dialkyl-substituted aromatic diamines, which may optionally be substituted on the aromatic ring by alkyl radicals, and having from 1 to 10 carbon atoms in the N-alkyl radical, such as N,N'-diethyl, N,N'-disecdecyl-, N,N'-dicyclohexyl-para- or -meta-phenylenediamine, N,N'-dimethyl-, N,N'-diethyl-, and N,N'-diisopropyl-4,4'-diaminodiphenyl methane, and/or substituted primary aromatic diamines and/or polyamines having relatively high functionality and possessing at least one alkyl substituent in the ortho position relative to amino groups, which inhibit the reactivity of the amino group as a result of steric hindering, which are liquid at room temperature, and which are completely or at least partially miscible with the component (b) at the processing conditions. For example, 1-methyl- 3,5-diethyl-2,4-phenylenediamine, 2,4-dimethyl-6-tert-butyl-1,3-phenylenediamine, and/or 3,3', 5,5'-tetraisopropyl-4,4'-diaminodiphenylmethane may be used either alone or mixed with diols and/or triols.

Z-H groups which are "phosphorylatable" are to be understood here as meaning Z-H groups which are capable of reacting under the conditions of acylation--Z-H groups whose reactivity has been impaired by steric hindrance or by inactivating groups are therefore intended to be excluded.

The steric hindrance of the hydroxyl groups, as mentioned above, serves to reduce the reactivity of the primary hydroxyl groups.

The term "basic sterically hindered lithium compounds" means any conventional organolithium compounds which have steric hindrance on the basic group (in order to avoid nucleophilic attack on the group-OR4) and which are derived from organic compounds with pKa values of at least about 9, preferably at least about 11.

The steric hindrance can be effected, for example, by branching or substitution at the carbon atom in the 1-position or by substitution in the ortho-position of a benzene ring.

Aromatic diisocyanates which are particularly preferred include those, for example, corresponding to the following general formulae (I) and (II): ##STR1## wherein R' and R" independently represent a group of the type noted above causing the steric hindrance of the isocyanate group; and in the case of the products corresponding to general formula (II), one of the radicals R' and R" may also represent hydrogen; or, in general formula (II), both R' and R" may also represent hydrogen if one of the isocyanate groups is in the ortho position to the bridge R"' or, if n=0, is in the ortho position to the left-hand aromatic radical;

The tendency to form polyureas which only dissolve with difficulty may be reduced by using diamines whose carbon frame does not correspond to the diisocyanates which are used and whose reactivity may be markedly reduced in a suitable manner, for example by steric hindrance.

If the hydroxyl group formed in the first stage of the reaction is not prevented, for example by steric hindrance, from undergoing further reaction, the second reaction stage of the process according to the invention gives rise to compounds containing excess isocyanate groups, sulfonic acid alkyl ester groups and urethane groups.

If the carboxyl group formed in the first stage of the reaction is not prevented, for example by steric hindrance, from undergoing further reaction, the second reaction stage of the process according to the invention gives rise to compounds containing excess isocyanate groups, sulfonic acid alkyl ester groups and amide groups.